Never Trust a Trailer/Live-Action TV

Examples of in  include:

"House: This test isn't exactly FDA-approved. Wilson: You committed a crime! Do something!"
 * A Brazlian cable TV trailer for a Dawson's Creek episode had Dawson saying the words I love you to Pacey, then leaning towards him. The voice-over even joked about Dawson borrowing some of Jack's genes (all the trailers in that network were really humorous and tongue-in-cheek) It turned out that episode had Dawson and Pacey reading one of Dawson's movie scripts, and he's not leaning towards Pacey, he's just reaching for the script. Though the reading the script scene was the first one in the episode, so for half a minute you thought Dawson was really professing his love for Pacey.
 * A trailer for the newest season of Law and Order Special Victims Unit used a shot of Olivia looking surprised with a shot of Elliot and Dani about to kiss, adding up to sexual tension at its max. In the actual episode, Olivia never saw the kiss, which was just an accidental quickie after the two had a few drinks. The trailer made more fans Squee than the episode.
 * SVU does this a lot, actually, putting small shots together in trailers or just taking them out of context and making them seem far more interesting than they actually are.
 * Another particularly bad SVU example: the trailer showed identical twin boys pressed against opposite sides of a wall, as the voiceover said "How can they tell which one committed the murder... when they have identical DNA?!" Not only was this not what the episode was about at all, not only was the aforementioned visual the last shot of the episode, not only was it that this spoiled the major twist of the episode (that the murder suspect's sister had been born a boy and raised as a girl after a botched circumcision), but it also spoiled the additional twist at the end of the episode (when the two collaborate to kill the doctor responsible). In fact, the question that the voiceover dramatically asks in the trailer is never even answered in the episode, and it's strongly suggested they'll go free.
 * One trailer had Cragen tell Olivia that she was "Dismissed", making many people think that she was going to get fired. Instead, while Cragen was pretty pissed at her, he was basically saying "Get out of my sight"
 * The Australian network who show this (Network Ten) basically make all their SVU trailers into one of these two versions:
 * Elliot does something to a perp that he shouldn't out of anger and it could cost him his career.
 * Benson gets too emotionally involved in a case, does something she shouldn't, jeopardises the case and it could cost her badge.
 * One of the USA Network’s standard promo for the show has what appears to be Elliot casually asking Fin what his favorite form of torture is while the two are relaxing and playing cards. However this seen never appeared on the show. The clip of the card game is from the episode Class while the torture question was from Uncle and asked to a suspect Elliot was trying to get to confess.
 * Those infamous official Korean Sherlock trailers that make it appear Sherlock and John's relationship is the focus of the series. Any of them.
 * Nowadays, ""On the Next..."" TV trailers will often include footage and plot points that don't actually appear for several weeks yet. This is Egregious in Prison Break-style shows with heavy continuity, as it can give the impression of the story progressing more quickly than it really does. Heroes is a major offender here; for example, it incorporated material from the entire first season into the trailer for the second episode.
 * Smallville is a worse offender. There have been several trailers that have cut one line of dialog into clips from several seasons past. The trailer for the seventh season finale was entirely a clip of Lex Luthor looking at the Fortress of Solitude. Not only was this teased two weeks previous, it was cut entirely from the episode it was shot for. Ironically, when a recent episode decided to reveal the adaptation of the Superman Suite, many fans believed they were being played (due to the show's "No Tights, No Flights" rule which is the whole reason why it took eight seasons to make something remotely close to Superman's tights) no one believed it. But the footage was used in the episode being teased.
 * Nearly every show nowadays does this after the season premiere and the voiceover usually explicitly says "This season on..." whichever show you happen to be watching.
 * In the middle of the Jasmine arc of Angel, an "On the Next..." centered around Angel and Fred kissing, with the announcer going on about how the crisis will drive them together... in the actual episode, the kiss turns out to be a Fake-Out Make-Out and no romance comes of it.
 * A trailer for the 2007 Doctor Who episode "The Family Of Blood" showed
 * The BBC One trailer for "The Waters Of Mars" ends with the Blatant Lie of someone knocking four times just like The Prophecy said, in the actual episode however, The trailer repeated the fist knock.
 * The ad for "The Doctor's Daughter" put way too much emphasis on a blonde girl performing handsprings through a row of lasers. The scene was actually just
 * The Australian trailer kept repeating "Father and daughter REUNITED!", even though Jenny was actually a newborn clone who took her first breaths in the episode.
 * That's likely to be more a case of Did Not Do the Research since The Doctor originally travelled with his granddaughter.
 * Let's not get started on "Turn Left"; let's just say that all the Doctor Who trailers tell us these days is the title of the episode and a few big shocks that WON'T be happening in the episode.
 * This only applies to the UK though. On the Sci-Fi Channel, the trailers frequently give away huge twists.
 * The Sci-Fi trailer for "Evolution of the Daleks" showed the Doctor standing below a hovering Dalek urging it to kill him
 * Suffice to say, no one was really surprised when the ads for "The End of Time" featured Wilf ominously informing the Doctor, "The Master is going to kill you!"...and in the actual episode--guess what?--
 * We can't even trust promo shots with Who as almost all the photos of The Eleventh Doctor's companion Amy Pond showed her wearing a police woman's uniform many were lead to believe that that would be her job -- turns out she's kissagram and that was just a costume she switched into when the Doctor showed up in her house. Although, given that it was a miniskirted police woman's uniform, others figured something like that was the case.
 * The trailers for "The Almost People" kept making out that was a villain, when in reality.
 * ABC Family's trailer of the Pretty Little Liars season final switched out which characters were in a car accident.
 * The episode previews for The Secret Life of the American Teenager are usually either uninformative or edit the footage together in a very misleading way. For example, there were numerous previews hinting that Amy and Ricky had feelings for each other or that they were going to get together long before.
 * Survivor has done this. Especially in Samoa, they tried to edit it so that people were thinking about eliminating Russell..except for some incredibly odd reason, seeing the episode brought out no talks about actually doing it.
 * One of the early seasons of Survivor featured an episode trailer that vaguely described some kind of horrific accident occurring, while flashing footage of crocodiles. An accident did actually occur (a contestant passed out due to smoke inhalation, was burned by their campfire, and had to be evacuated), but involved no attack by a wild animal of any kind.
 * One Star Trek: Voyager episode trailer was particularly bad in this respect, being designed around the line "He violated me" in such a way as to make it sound very much as though Seven was going to be raped by a crew member; the trailer even featured a "Who did it?" sequence with flashes of various male crew members' faces. The actual episode, however, was just about an alien culture trapping her in a laboratory for study and stealing some of her nanoprobes. The plot does play at Does This Remind You of Anything?, with Borg nanoprobes replacing date rape, but it was still incredibly misleading.
 * In regards to Voyager, a website designed to nitpick the show refers to this phenomenon as PAL, for Previews Always Lie. See here.
 * In a comparatively minor case, SPIKE's trademark preview for Voyager makes it out to be an action-packed, phasers-firing thrill ride. "Network for Men" and all that.
 * Voyager's action quotient is such that it's not entirely unwarranted. Now, when they tried to do the same with The Next Generation...
 * A trailer for some season 7 Voyager episode during its run that featured Kim saying "Ambassador Spock" in a shocked voice, leading me and many in the audience to tune in in hopes that everyone's favorite Vulcan would show up. As it turns out, Spock was mentioned briefly in one conversation and that 'shocked take' wasn't even in the episode.
 * Another trailer similarly name-dropped Captain Picard; the interview review The Cynic pithily remarked "dropping Picard's name will not get them Picard's ratings."
 * The trailer for one Deep Space Nine episode showed the Enterprise being destroyed... or so we thought. Turns out it's a ship of the same class, called the Odyssey (Justified, maybe, in that Word of God says that the point of it happening in the episode was to tell the viewers "This might very well happen to the Enterprise" and to make them think of the familiar ship in that situation).
 * A recent trailer for Deep Space 9 on the CBS Reality channel showed how to do it when you've no idea which show you're talking about. It went on strangely in poetic terms, including the line "When the universe sleeps...Enterprise wakes (and basically saves us all)." Huh?
 * The trailer for the Enterprise episode "Cogenitor", about an alien species with 3 genders, made it look like a comedic sex romp by focusing solely on the brief comic relief moments in the episode, such as Phlox offering to show Trip photos of tri-gendered sex and Malcolm awkwardly flirting with an alien. In actuality, it's one of the darkest episodes in Trek history, raising complex questions about human rights and moral relativism, capped off with a deeply tragic ending.
 * Final Star Trek spin-off example: UK TV channel Virgin 1 markets Star Trek: Enterprise on the basis of the handful of relatively sexy moments that make up the 4 seasons. While it might have featured more blatant sexual situations than the previous Star Trek series, the show was still pretty tame by most modern standards.
 * During the early 00s, the British Soap Opera Eastenders featured a number of intentionally misleading trailers. For example, one suggested that Saskia would kill club owner Steve; when the actual episode rolled around, the exact opposite happened. Much later, after Matthew was framed by Steve for Saskia's murder, a specially filmed trailer suggested that Matthew would get his revenge by setting up explosive death traps -- in reality, his actual revenge plan was slightly less violent.
 * FOX's promo monkeys tried to make a contestant's brief moment of discomfort on Don't Forget the Lyrics much more dramatic than it actually was. (Source)
 * And also promoting the same show, they managed to combine this with Trailers Always Spoil: The promos said that a contestant would win more money than anyone else, and said contestant only actually tied for the biggest win.
 * Played with in Arrested Development, in which the clips at the end of each episode were almost never actually featured in the next, but sometimes became important in their own right.
 * Sometimes those clips would appear on the next episode, but the viewer would never expect it because of so many falsities, they would never expect the truth.
 * Also, in one third-season episode, trailers advertised 3-D, that "the shocking final moments" would be live, and that "one of these people will die". Well, they did come through! ...In underwhelming ways:
 * On the 3D, it lasts for about one shot.
 * The old racist lady dies. The narrator made a point to mention it.
 * For the final scene, only that one 5 second part was done live.
 * Sadly, this trope may have led to the show's cancellation. The original TV-spots didn't quite present the show as they should have.
 * iCarly: Done exceptionally badly for the episode iStart A Fan War. After months of fandom speculation that this episode would be a ship-centric episode that would involve shipping development, the first trailer appeared to confirm that not only would it involve the ships (using both popular ships by their Portmanteau Couple Name), but that it would actually end the Ship-to-Ship Combat in regards to which became canon. This was not what happened, as the show ended with an Author Filibuster about how shipping was not what the Word of God wanted to focus on. Obviously, neither ship was even vaguely developed positively.
 * The Word of God released a blog post later that made it appear to be a miscalculation by the marketing department of Nickelodeon, who either didn't realize that the episode didn't actually do anything they claimed, or They Just Didn't Care, and release the trailer like that to hype up the episode.
 * Inverted with a Word of God confirmation that the trailer for 'iOMG' isn't the same as the iSAFW debacle and something major does happen.
 * Victorious has also been guilty of this
 * Nickelodeon aired promos for "Crush Week" starring Justin Bieber and the girls from the cast of Victorious. One thing present there was a new episode of said show called "The Wood". The promos hinted the possibility of Tori and Beck becoming "more than friends" (read: a couple), showing a scene of her calling Beck on her phone, expressing love and offering to tickle his tummy. Almost immediately, fans of the Beck and Jade pairing that is currently present on the show raged and bashed the thought of said idea. Then, when the episode aired, it had next to nothing to do with love or pairings. It was a fusion of two clips-one with Tori calling her aunt about their puppy, another with Beck ordering a pizza. This made Jade think Tori was hitting on Beck, causing them to ensue hilarity. Thus, the Beck/Jade shippers got worked up for nothing.
 * Although at least that was what actually happened in the episode itself, with a reality show cutting those two conversations together in-universe, it wasn't created by the promo department.
 * The promos for "Jade Gets Crushed" make it seem like the premise of the episode is Jade going on a rampage. Really, she's significantly nicer in the episode than usual.
 * A preview for the Lost episode "Stranger in a Strange Land" promised that three huge questions would be answered in it. These turned out to be the meaning of Jack's tattoos, what happened to the children the Others kidnapped and what happened to Cindy the flight attendant. Those last two have the same answer so many viewers argued they shouldn't count as separate questions, and it's not like many people were chomping at the bit about the first one either. The producers immediately said they never intended the episode to be one that was full of reveals like that, and blamed the network for unduly raising the viewers' hopes when it became one of the show's most unpopular episodes.
 * A preview for the episode "Outlaws" made it look like Sawyer was pointing a gun at Jack. The clips of Sawyer pointing the gun and the clips of Jack looking scared were actually taken from two entirely different scenes. Sawyer spent the entire episode hunting a freakin' boar.
 * Season six has done this. The trailers for the first five or six episodes mixed footage from all of them together, in a attempt to make a fairly slow moving and talky arc seem more exciting. Jack destroying the mirrors in the lighthouse was in pretty much every trailer despite not happening until episode five. The ad for "The Last Recruit" showed aiming a gun at  and firing; in the episode, he doesn't fire it and 's fate is left ambigious.
 * Trailers for "Dr. Linus" made it look like Ben was going to die in it. Ben
 * The marketing for Kings ignored the heavy religious overtones and the fact that the story was based loosely on that of King David. NBC apparently was afraid that religious audiences would find fault with their retelling, and that secular viewers wouldn't want to watch a show with its basis in the Bible.
 * A preview for an episode of ER where a main character seems to suffer a very serious heart attack, with ominous music and worried onlookers. In the actual episode it turns out to simply be gas.
 * At the end of a season finale for Buffy the Vampire Slayer, there was a long preview hyping the next season's premiere, saying that Buffy would face her deadliest, strongest, most legendary foe ever... Dracula. The hype blitz continued during the entire off season, with every Buffy rerun containing a promo for the Buffy vs. Dracula showdown, commercials for it even ran in unconnected commercial spots, often during primetime. In all, it was built up as Dracula obviously being the Big Bad for the coming season, or perhaps even multiple seasons, so epic was the ad campaign for the upcoming meeting. When the episode finally came... it was a one-shot, essentially a gag episode, where Dracula's arrival was treated largely as a joke and Buffy doesn't actually defeat him, but essentially mocks him into laying down and playing dead. He was never heard from on the TV series again, reappearing only in comics once or twice. Hard to say whether it was just a really deceptive ad campaign or a rather mean-spirited Take That.
 * To be fair, all Buffy seasons after the first had featured surprise supervillains, so serious fans would have known better.
 * Though it did cause the most unique version of Dracula ever in Season 8. He's implied to have a huge crush on Xander and helps them just because Xander wants him to.
 * And it also allows him to give one of the best speeches in the series, resulting in a supreme Let's Get Dangerous moment as the "old man" reminds the young upstart exactly who Vlad Tepes the Third was.
 * There's a trailer for Supernatural which makes it look like Dean set Jessica on fire.
 * And let's not forget the one that makes it look like the Crossroads Demon seduces Dean. And the episode summary even said that.
 * The trailer for the US version of Life On Mars is shot like a Starsky and Hutch parody. Seriously, watch it.
 * This seems entirely in keeping with the UK version.
 * A trailer for an episode of Hell's Kitchen Season 4 did a rather spectacular version of this. The trailer showed that one chef sliced off a portion of his thumb, the team couldn't find it, and mentioned that two professional critics were attending that night's service - with the narrator all but saying that the severed portion of finger would end up on a critic's plate. As it turned out, the finger incident happened in the first part of the show, and was already resolved by the time dinner service rolled around - there was never any risk involved.
 * The trailer for the final episode of Season 1 featured a clip of Michael yelling "Piss off!", but it was almost made to look like he was fighting with Ralph; when the episode actually aired, it was revealed that Michael was simply imitating Chef Ramsey's mannerisms, and Ralph was laughing along with it.
 * Season 5 does this a lot. Near the end there's a cliffhanger that's resolved immediately the next week.
 * Any time you see an ambulance or fire engine in the "Next on". Expect it to be either A. a complete over-dramatization of something minor (with no ambulance or fire engine in the actual episode) or B. part of a challenge.
 * Bravo is notoriously bad for doing this with their reality TV shows. Misleading episode descriptions, cut n' paste editing, mismatched dialogue--they've used every trick in the book.
 * An interesting case on Battlestar Galactica: the trailer featured D'Anna this would have been a major case of both Trailers Always Spoil and Lying Creator (as showrunner and producer Ron Moore had officially declared that ).
 * A preview for an episode of Stargate SG-1 revolving around the team being trapped in an unpleasant version of a Lotus Eater Machine, with the trailer using Carter's line "How do we know this is real?" as if it were a serious question and dramatic concern. In the actual episode, this is just the set-up for a final joke to cap off what's otherwise a particularly dark episode.
 * For several weeks there, the trailers for Stargate Atlantis alluded to replicator involvement. "Or is it a Replicator trap?" "Is he really back from the dead, or is it another Replicator?" Needless to say, Replicators weren't even mentioned in those episodes.
 * Stargate Universe follows the trend for a recent episode. Footage of the crew running down the hallway is accompanied by the usual urgent voice overs, as if they're running to avert some disaster. In the actual episode, it turns out it's just the crew working out during the opening montage.
 * Two particular examples for the original Stargate SG-1. One, where it was hyped up that a team member would end up dying and a clip of O'Neill falling to the ground wounded in battle was shown(It ended up being the doctor who died). The second was set up with Carter finding herself alone on a ship with only illusions to help her. The trailer made it look like she and O'Neill would end up kissing, but in the actual episode it was only a fantasy of hers that passed through her mind for a second- two at the most.
 * To be fair, in the first example, the episode itself actually implied that up until the last five minutes or so. So it wasn't just the creators of the ad, but the writers as well who intended the audience to be misled.
 * The trailers for the NBC miniseries Merlin implied there was going to be a big huge battle between the title character and Queen Mab. In reality, while there was some shrieking, a few fireballs thrown, and other cool magical effects, the whole thing actually ended with . A very effective and creative way to defeat a villain, but it was probably rather disappointing for those who wanted to see Mab turned into a crispy critter.
 * On the subject of Merlin, a trailer for one episode of the BBC series had Merlin dramatically reveal to the court that he was a wizard. In the actual episode, no one believed him and the scene had no impact on the plot.
 * The trailer for another episode made it look very, very much like Arthur was going to find out about Merlin's magic. And just before the episode started, the announcer said 'it had to happen eventually!'. Everyone got very excited about this. Turns out what Arthur saw was just ambiguous enough for him to believe Merlin hadn't done anything.
 * The Sopranos tended to do this a lot, with the trailers playing up the mob violence that was rarely the center of the upcoming episode.
 * The trailer for the final episode on A&E promised "You won't believe how it ends!" In case you were one of the people who missed the controversy at the time,
 * CBS had a promo for an episode of CSINY, "All In The Family" with Danny shielding a woman from another person with a gun, then the screen cutting to black and the sound of a gunshot. In reality,  the gun sound was in fact a sound effect added in.
 * The 2009 Christmas special for The Big Bang Theory featured a clip of Leonard's mother kissing Sheldon as if it were a huge plot point. In the actual episode, she was drunk and curious. It was more of a gag than anything.
 * Promos for the third season finale did this as well. They had the announcer ask what the guys would do for the finale with Sheldon saying "We're going to blow up the moon." In the actual episode, Penny's date asks if that's what they're going to do and Sheldon actually says "You'd be crazy to think we're going to blow up the moon."
 * Sci-Fi Channel actually used expectations about never trusting a trailer to its advantage for the fourth episode of season three of Eureka, and at the same time did slip in a little bit of a lie. The trailer proclaimed "One of these people won't make it through [the episode]", including flashing up a character we'd never seen before, clearly a one-shot throwaway character, using your expectation that they threw him into the preview to be technically correct when one of "these characters" didn't make it through.
 * A rather dated example: The original "On the next" trailer for the War of the Worlds episode "Candle in the Night" showed the aliens desperately tracking a rogue device to stop it falling into the hands of the humans, asking, "Can the team use the aliens' own episode against them? A View to a kill, on the next episode of War of the Worlds!". Answer: No. Because they're not even looking for it: it's a Bottle Episode about the team organizing a surprise birthday party. The events of the trailer refer to a throwaway B-plot about the aliens trying to find a lost probe.
 * A trailer for a Dexter episode asked "Which one of these suspects is the ice truck killer". The "suspects" seem to have been chosen completely at random, two are very well established characters who couldn't be the killer barring some bizarre Twist Ending. Another has the notable handicap of being dead. The process of elimination would seem to point to the fourth suspect who, having been only introduced in the previous episode, seems the natural candidate anyway, but since whoever made the trailer has clearly not watched a second of the show it would probably be hopelessly naive to think so. Another on asked if this was the episode were Dexter would be found out, which only did not happen, but had absolutely nothing to do with the plot.
 * Australia's Network Ten does this with all its commercials. Another example is its adds for Burn Notice, which always end by asking if this is the episode where Michael's plan fails, followed by footage of an unrelated car exploding from later in that episode.
 * Australian television always markets shows like The World's Worst Drivers as if they're comedies, when almost all take the form of overly tense When Animals Attack-style shows.
 * In the trailer for the fifth season opener of Grey's Anatomy, Nurse Rose told Dr. McDreamy that "I'm carrying your child." In the actual episode,
 * And in the trailer for the seventh season finale, Meredith walks in on a cleaned-out bedroom after having a fight with Derek, during which he said he couldn't live with someone who'd . In the actual episode, the room isn't even Derek's, and Meredith actually asked that character to move out earlier in the episode.
 * Happens far too often on House. For example, the trailer for an episode during the Tritter arc had the following exchange:

"House: This test isn't exactly FDA-approved. [the test goes exactly as planned with no ill effects] House: [much later] Hey, Wilson, Tritter is still bugging me about my drug habits, which, As You Know, I did some illegal stuff to support. Wilson: You committed a crime! Do something! House: I don't wanna, cause I'm a Jerkass."
 * The reality, however, was more like this (somewhat paraphrased):

"Author: You really think I believe you're going to help me commit suicide? House: I'm giving you a choice. Turns out, he was just trying to prove that she was still suicidal to extend her psychiatric watch."
 * Also, the trailer for the season 5 ep. Lucky Thirteen made Thirteen's sex scene look way hotter than it was
 * Can't forget the various romances that also were teased to come to a culmination including House making out with Cameron in Season 3.
 * Another part of the trailer for this episode shows House saying he has brain cancer
 * The end of Season Five did this the most because all the revelatory stuff it showed such as House sexing up Cuddy
 * This trope has been so overdone for House, anytime you see House getting "some" in a trailer it would be safe to assume shenanigans.
 * The recent episode with the suicidal author had this exchange:

"...Hammond falls on a valley..."
 * The ad for the sixth season, showed Cuddy with House's voice saying that she had said yes, but he heard no which could be seen as that House had proposed to Cuddy and she had said yes..
 * Season 5 of Anthony Bourdain: No Reservations was bloated with this. Every episode pointed out that he was going to have a bad time at his destination but on the actual show, it was always just a minor moment of discomfort that took place in the first half of the episode, surrounded by Tony loving the place.
 * A "On the Next..." trailer for Being Human (UK) showed (in order): A woman looking into her hand mirror and realizing that Mitchell has no reflection, A Torches and Pitchforks mob of neighbors shouting and throwing things at the outside of the main characters house, and George saying "We were kidding ourselves to believe we could fit in here. We.. are MONSTERS!". The not so subtle implication was that the Vampire, Werewolf and Ghost would all be outed and they'd have to deal with the ramifications of that. In the episode itself Mitchell was accused of pedophilia because the woman's son accidentally borrowed a vampire porn/snuff film from him. The Masquerade remaines unbroken, except for the boy and his mum finding out about Mitchell at the end before promptly leaving and telling the neighbors that they made a mistake.
 * In the network promo for the Season 4 episode of The West Wing "Election Night," there is a shot of Democratic strategist Will Bailey standing outside the campaign office in a thunderous rainstorm, shouting "NOOO" to the high heavens. In the actual episode, he is in fact shouting "NOW" in an attempt, however serious, to predict (and possibly cause?) the torrential rain that begins seconds later, thus leading to depressed voter turnout and increasing the chances that his liberal candidate, who is dead, might actually win in conservative Orange County.
 * A trailer for an episode of the New Zealand TV show Go Girls has a main character being told by her boyfriend that she's fat, ugly, and that he's gay. In actuality, this was a daydream of what she was expecting him to say-- what he actually does is ask her to marry him.
 * A Desperate Housewives preview ended by promising "a twist so shocking, we can only hint at it," followed by the first line from the chorus of Kate Perry's "I Kissed a Girl": "I kissed a girl, and I liked it." The obvious implication was that one of the housewives would become a lesbian, or at least question her sexuality for a while. The episode did at least follow through with two lengthy girl on girl kisses, but it was part of a minor comic relief subplot where Susan's lesbian boss mistakes her for being interested, and the misunderstanding is entirely cleared up at the end never to be brought up again.
 * Not sure if it counts since it wasn't exactly a trailer, but an animated ad on the internet.
 * The fourth season of Oz went on hiatus following the stunning death of Simon Adebisi at the hands of the formerly pacifistic Kareem Said. When the show returned, one of the promos featured Said shouting "Adebisi lives!" In the actual episode the line didn't signify that Adebisi was actually alive; Said said it after killing someone else as a statement that his years in prison had turned him into a violent murderer just like Adebisi. It was still a powerful scene, but the previews had viewers feeling ripped off anyway.
 * Trailer for the seventh season finale of Monk. Narrator: "You'll never believe what he finds [at the site of his wife's murder]..." What did he find?  Though to be fair, no one believed it.
 * The Season 5 finale of Medium is being billed as the main character's "last vision". Which it is...on NBC. The show is moving to CBS next fall.
 * During the 2009 opilio crab season, the preview for the next episode of Deadliest Catch included the captain of the Cornelia Marie calling for a Coast Guard helicopter, leading the viewer to assume an emergency. The reality? The captain was calling to ask what the ice conditions were like while preparing to leave the harbor.
 * The trailers for Secret Girlfriend implied that the show would primarily be about two pervy slacker guys trying to get women to perform activities of a sexual or suggestive nature, completely ignoring the fact that the viewer is experiencing the actual protagonist's experiences (kind of like Being John Malkovich) and is about the nameless protagonist's attempts to deal with a psycho near-ex-girlfriend who won't stay broken up, a cute girl he likes but wants to protect from the first woman, and the zany antics of his two best friends (the aforementioned slackers).
 * Cracked.com has this trope listed as #1 of the "5 Cheap Tricks TV Shows Use To Keep You Watching" found here.
 * This preview for the NCIS season six finale made it look like Ziva was going to kill Tony on her father's orders. Pretty shifty of CBS, but at least the episode itself was good.
 * Under Covers, which has a giveaway title as it is, was played out as being an actual hookup between Tony and Ziva. It's really too bad that the big reveal was five minutes in, and that it was a repeat.
 * The trailers for Swedish 90s miniseries Nattens barn made it seem like a vampire/supernatural story, while it was in fact a perfectly realistic series about a Romantic Two-Girl Friendship between two Goths.
 * In its early days, Sky One used to have a single set of clips for an entire series which they played every week, regardless of which episode was to be shown at the advertised time. The result being of course that the episode usually had nothing to do with the clips you saw in the ad.
 * Can't say anything for the trailers (I wasn't a fan at the time), but the Verizon FiOS info for a particular episode of Bones states that the cast is working undercover at a bar to help solve a case; additionally, ads hyped the fact that Booth and Bones would wind up in bed. Actually
 * The trailers were, in fact, just as deceptive for that episode.
 * FiOS's info is at it again: All of Tom Hanks' appearances on talk shows in March 2010 are descibed as "Toy Story 3's Tom Hanks" even though he's doing PR for The Pacific while Toy Story 3 doesn't bow until June and never gets mentioned. Clearly, FiOS' info writers know what their viewers really like to watch.
 * In the lead-up to the Mighty Morphin Power Rangers 3-parter "The Wedding," in which Lord Zedd and Rita Repulsa get married, Fox did a promo of the "Someone's getting married...who could it be?" variety, and seemed to suggest that it might be one of the Rangers, perhaps Billy, or even Tommy and Kimberly! Never mind the fact that they're all supposed to be teenagers...
 * One promo for an episode of One Tree Hill outright stated that Peyton was going to once again have feelings for Nathan. Cue the episode where Nathan and Peyton become partners on a project and spend the rest of the episode having fun with no mention of romance at all.
 * During the middle of its run Red Dwarf had an intro sequence that made it look more like some kind of high-adventure show than an irreverent comedy with a sci-fi backdrop.
 * On a sleazier note, a trailer for the less-than-stellar dramedy Wildfire showed one character inviting another to a Two-Person Pool Party, with a clear implication of sex. Since this was on primetime TV before the Watershed, in the actual episode the line was immediately followed by a blunt refusal.
 * One episode preview for Airwolf has Dom complaining about how low they're flying, followed by a cactus being splattered against the window. The cactus was removed from the actual episode.
 * During its last few seasons, Home Improvement was notoriously misleading with its advertisements. In one particular episode, Jill catches her her oldest son Brad in a compromising position with his girlfriend Ashley. The advert shows Brad getting caught in the act, followed by Jill asking, "Is Ashley pregnant?"; we see Brad's serious facial expression--and a shocked reaction from his mother. The reality?  Not that you'd know it, of course.
 * In another episode from a later season, Jill hires a professional (played by Tom Wopat) to install granite countertops; the handyman turns be the same guy who once flirted with her at the gym and tried to ask her out. Nothing happens between them, and Jill actually fires the guy because his behavior makes her so uncomfortable. The advertisement, on the other hand, shows the two of them kissing passionately (which actually happened during a Dream Sequence in a previous episode), Jill tearfully confessing "He kissed me!" (which he did--briefly, without her consent, right before she fired him), and Tim opening the front door and coming face to face with the flirtatious handyman (who actually just came back to get his tools).
 * During the hype blitz in the lead-up to the 2010 Juno Awards, the trailers stated that Nickelback and Hedley would be giving performances. Neither of them did. Nickelback didn't even show up (though that may have been caused by the fog...), but Hedley did and even PRESENTED ONE OF THE AWARDS and TOOK PART IN THE FINAL PERFORMANCE (Wavin' Flag, FYI).
 * Most trailers for My Name Is Earl will always show footage from the flashback scenes, giving you the impression the show is just about an idiot doing stupid things.
 * This isn't really deceptive, the show got a lot of mileage out of pretending it didn't approve of Earl being a colossal jackass for Rule of Funny because he could fix it in the non-flashback part of the episode.
 * The trailer for a recent episode of The Big Bang Theory had the narrator announce "this is the episode you've been waiting for", then showed scenes of a hot woman in the guys's apartment and a scene of Sheldon giggling, making it look like he was attracted to her. Needless to say, or it wouldn't be in this category, Sheldon had no romantic interest in the woman whatsoever (she was a fellow physicist he invited to stay with him) and the giggling was taken out of context. (Said woman did have sex, but with Leonard, and later, Raj).
 * (But not Howard, or for that matter Leonard, Howard and Raj at the same time. Though not for lack of trying.)
 * Possibly overlaps with Tonight Someone Dies: an episode of Cold Case had a plot where one of the detectives had gone missing and the others were looking for him. The trailer had a scene where they encounter a body, with one of them pulling away the sheet and reacting appropriately..
 * One episode of So You Think You Can Dance was promoted by FOX with a clip of Nigel Lythgoe shouting "Get off the stage!", suggesting that he was so angry at a contestant's performance he wanted them to leave. As shown in the actual episode, however, he was shouting out of enjoyment, and telling them to get off the stage because they'd made it to the next round.
 * One of the later episodes of the Australian version's first season was promoted with the audience booing and leaving the set, with the voiceover saying that someone would perform so badly that the audience would walk out. What actually happened was that the judges asked the audience to leave for a short amount of time (I can't remember why, I think it had something to do with the voting).
 * At the end of the cliffhanger finale of Kamen Rider Decade, a fifteen-second trailer for The Movie that would end of the story aired. The trailer shows an Evil Twin of the main character, the sidekick (who closed out the series Brainwashed and Crazy) with his arm buried up to the elbow in The Rival's gut, the female lead trying to kill the hero with a sniper rifle, and more. In the actual film, none of this happened as depicted, though two concepts (the female lead opposing the hero and a tagalong character becoming a Rider) were merged together. It didn't help that it looked like a much better finale than what we actually got.
 * The trailer for Kamen Rider Faiz made us believe that there world be a lead female Rider for the first time. It was very convincing.
 * America's Got Talent usually includes a teaser featuring a mediocre contestant crying during an elimination round, bookended with clips of the judges admonishing someone. 95% of the time, the contestant is actually crying Tears of Joy because they're so happy to have made it through.
 * Teasers for upcoming episodes also sometimes feature contestants who never appear or only pop up weeks later.
 * The commercials for the U.S. version of Masterchef only featured Gordon Ramsey as the judge. They completely failed to mention that there's two other judges involved in this.
 * Teen Nick mastered this trope for Degrassi promos. Season 10 has a lot of blatant examples. Fiona standing at the edge of the roof (is not a suicide attempt, she just finds it dramatic to think on the roof). Anya's pregnant (no she's not), Clare's getting a boobjob (no she isn't). In the final episode of 2010, they showed Jenna looking like she was in labor at a party(she wasn't) Then they continue with this in the trailers for the 2011 premiere, as if everybody forgot what the actual situation was. The best being an ad playing on Ship Tease, with the two actors practicing on the copier for the show. That couple never happened in the series, ever.
 * Everybody Hates Chris did this all the time in the later seasons. They weren't even subtle. No editing, just stuff that didn't happen. One episode trailer had Drew in a school talent show, getting booed off the stage and people throwing things at him. Never happened, not even if a dream before hand about how things might go. He just showed up and rocked.
 * The Australian promos for Veronica Mars described the show as "What would you do if your best friend was murdered, and YOU were accused of being the murderer, and the whole school hated you?", something that the main character was never accused of in the show.
 * In the midseason finale of Caprica, Amanda Graystone attempted suicide by jumping off a bridge. In a trailer for the next half-season, her husband Daniel was seen angrily throwing a holographic avatar of Amanda to the couch and shouting "I want you to be real!". The obvious interpretation was that Amanda had actually died and Daniel was trying to create a Replacement Goldfish (as had already been successfully done with his daughter Zoe and Joseph Adama's daughter Tamara), making this a case of Trailers Always Spoil. Except, when the half-season aired, it turned out that.
 * In the previews for the Castle episode "Nikki Heat", we see Castle hold a diamond ring in a box and ask an unseen person "Will you marry me?". In the actual episode, Castle is just giving Ryan advice on how to propose to his (Ryan's) girlfriend.
 * Newer How I Met Your Mother trailers in Germany feature only various scenes of Barney, letting it appear as if he were the main character.
 * Top Gear plays with this, especially since season 3. Their previews are not only useless, but also mislead on what the episodes actually mean.
 * Top Gear plays with this, especially since season 3. Their previews are not only useless, but also mislead on what the episodes actually mean.


 * Top Gear Season 16 had a preview which went, "Tonight! I wear a hat! Richard wears a hat! And James! Wears a hat!". And true to their word, they all did!
 * Glee does this a lot by leaking songs for the upcoming episodes...reading too much into the lyrics and what they may or may not indicate about your favorite couple is not advised.
 * Pawn Stars and American Restoration both History Channel Shows, do this for their opening previews. They mix and match scenes and voice overs to make up events that never happen in the show. For example making something seem to be a fake in Pawn Stars or breaking something in American Restoration.
 * One trailer for WWE Tough Enough featured some WWE Divas as guest stars, and showed one of them slapping Jeremiah with the implication that he'd done something untoward to deserve it. In truth, he was just drunk and being goofy, and asked to be slapped in a moment of euphoria.
 * Mad Men's main character Don Draper changed identities with a dead guy during the Korean War and has been hiding it ever since. A promo for the season two episode "A Night to Remember" had Joan Holloway announcing, "Someone people think is dead is not dead," in a context intended to make it look like she was going to find out his secret and out him (or threaten to, or something). In fact, she'd spent the episode reading TV scripts for work and was talking about an upcoming storyline on a soap opera.
 * It is pretty much a guarantee on the HGTV reality show Design Star that whoever looks like they are in trouble at the end of the episode is fine, and vice versa. For example, in a recent episode, the judges say, "This is not your best work" and it cuts to a dismayed-looking . In the actual episode,.
 * In October 2010, Wheel of Fortune ran a trailer hinting at a $1,000,000 win a few days later. It showed a contestant hitting the Million-Dollar Wedge (which must be taken to the Bonus Round, where one of the Bonus Wheel's 24 envelopes is replaced with a $1,000,000). The contestant in the clip actually lost the Wedge to Bankrupt, and with it, the chance at getting her million.
 * Late in the run of Hercules: The Legendary Journeys the trailers practically guaranteed that a particular episode was the finale of the series. Turns out Hercules did retire...for about five seconds.