You've just happened onto an absolute steal of a deal. Seriously, the guy apparently doesn't know what he has, and his asking price is far too low. So you buy it, sight unseen. Or it's simply something that you want, and the price is decent. Again, you buy it, sight unseen.
Then you unwrap it and take a closer look. And it's not what you thought you were buying. Maybe it doesn't work nearly as well as the seller said it would. Maybe it doesn't work at all. Maybe it isn't even close to what was described. You just bought a Pig in a Poke.
Purchasing one may make you a Unwitting Pawn, if some evil organization is involved. A Pig In A Poke usually doesn't do any harm to the buyer, excepting of course for his wallet. For objects that actually do harm the purchaser, see Artifact of Doom and Artifact of Death.
The old Latin saying "Caveat Emptor"* goes to show that this trope is Older Than Feudalism. Fables about fools purchasing worthless junk at a premium can be found around the world.
The Trope Namer is a Middle Ages confidence trick wherein a con artist would sell somebody what is supposed to be a suckling pig in a sack or poke. In fact the hidden meat would be a cat. The same con gives us the phrase "to let the cat out of the bag". Known in Spanish as "dar gato por liebre" (giving a cat instead of a hare) after the Medieval practice of selling cats instead of hares for food. Unlike the pig, hares and cats look quite similar when skinned (and yes, That Poor Cat).
A Pig In A Poke that specifically uses illegal items, resulting in the buyer having no way to involve the authorities without getting in trouble themselves, is a Beat Bag.
If the seller shows you what he's selling, but then uses sleight of hand so that isn't what you actually get, its Good for Bad.
Compare Violin Scam, where the buyer is convinced that he's scamming the seller by the seller's confederate. See Mock Guffin when the hero discovers that the MacGuffin is a worthless and/or insignificant object.
- Doctor Doom often did this to Latverian nobles in his early years, with help from his Gadgeteer Genius qualities. For example, he sold a device that he claimed was a violin that played amazing music regardless of the player's skill, but was actually a remote-controlled radio.
- The basic plot of Burn After Reading is that a few morons discover a manuscript for the written memoir of a former intelligence agency employee and, falsely believing it to contain classified information, try to sell it to the Russian government. The Russians can't be fooled though and reject what turns out to be useless drivel.
- At the end of the 2007 St. Trinian's, Flash Harry sells "Girl With A Pearl Earring" to Carnaby for £500,000... which turns out to be a reproduction painted by Miss Fritton. The girls "find" and return the original, getting another £50,000 reward.
- In Harry Potter, leprechaun's gold vanishes shortly after you pick it up, rendering it completely worthless except for screwing over people you owe money to (which is exactly what it gets used for). It does have other uses - namely, some magical creatures are attracted to gold, which means leprechaun gold can be a cheap substitute.
- Conversed in Neil Gaiman's American Gods: Wednesday is talking about some of his favorite grifts, one of which involves a violin, two grifters, and an upper-class waiter as The Mark.
- In Roughing It, Mark Twain describes a type: combing an otherwise worthless mine for one tiny chunk of rock containing silver or gold, presenting it to the assay office as an "average" sample, then selling shares in the now grossly overvalued mine.
- In Haven, Duke presents a chef with a box containing an exotic ingredient and names a price. The chef then has to decide if he wants to buy the item without seeing it first. Duke knows what the item is worth but he is not really scamming the chef. They are old friends and it's a game they have been playing for years. Sometimes Duke will overprice the item and sometime he will underprice it making sure that his friend will not feel taken advantage of.
- Twice in the first episode of The Steven Banks Show, titled "Rock Auction." During a PBS fundraising auction Steve buys what he thinks is John Lennon's guitar but it's only the case...and it was Julian Lennon. Meanwhile Peter Tork is there too, having bought one of his own Monkees shirts (which a fan had ripped off of his body years earlier). But when they show it to him it's much too small: "That one is Davy's!"
- A particularly notorious Judge Judy case involving an ebay scammer had the scammer advertise that she was selling two mobile phones, and what The Marks actually received were two pictures of the phones, with the scammer being very careful to say on the advert that the buyers are bidding on "what [they] see in the photo" allowing her to claim she hadn't actually deceived the marks. Unfortunately for the scammer, between appearing on the show (where Judy can do pretty much whatever she wants and isn't as vulnerable to Loophole Abuse as another court might be,) slamming down hard on Judy's known Berserk Buttons (not having a job, making working people lose the money they've earned, and treating Judy herself as if she's an idiot,) and being less careful with the product description (she gave the weight of the product as 4.90 oz, and since the two photos the marks got sent obviously weighed far less than that, the Loophole Abuse itself had a gaping loophole,) the scammer simply got one of the most vicious humiliations in the show's history in front of 10 million viewers while the marks got compensated the maximum $5000 Judy's allowed to rule.
- This comes up in the folk song "Quare Bungle Rye." Jack thinks he's getting good whiskey, but the seller slips him a baby in a basket instead and runs off.
- In Knights of the Old Republic II a salvager tries to sell you a holocron for 500 credits. When you ask to see it, he says that it doesn't work that way: he doesn't know the item's real value, so you would both be gambling on this deal. (it turns out to be fake)
- This comes up twice in Pokémon Red and Blue:
- At one point, you're offered a Farfetch'd, which can be found nowhere else, for an incredibly common Spearow. The catch is that Farfetch'd's battle potential is nowhere near what Spearow's is, especially when you factor in that Spearow can evolve into the much stronger Fearow. This was entirely intentional by the developers, as Farfetch'd is based on a proverb about a duck with an onion leek, which can refer to either a stroke of luck (finding a meal that comes with its own seasoning) or being an easy mark for a con (being the duck itself).
- Much earlier, you're offered the chance to buy a Magikarp long before you'll be able to catch one yourself, but Magikarp is absolutely worthless in battle. But this one gets subverted; it's the Trope Namer for Magikarp Power for a reason...
- Many in-game trades throughout the series seem to count as this, mostly due to the fact that their stats, genders and nature are usually fixed. The only thing that varied was the level, which will be the same as the Pokémon you just traded (This is also fixed in Gen V as well). Generally, these stats are mediocre at best. One trade in Pokémon Diamond and Pearl promises you a Haunter (which evolves into Gengar by trading) in exchange for a Medicham, which can be found right nearby; but when you trade the Medicham for said Haunter... It doesn't evolve because it is holding an Everstone; an item used to specifically prevent evolution.
- In South Park when the boys are involved in a tooth fairy scam, one of the boys working for Cartman buys what he was told were Chinese teeth, but are actually cat teeth.
- The Hector Heathcote Show had an episode called "Pig In A Poke," which dealt with the Louisiana Purchase. Heathcote and his dog Winston are sent to meet Lewis and Clark to see if the deal is worth it. The villain Benedict and his stooge pretend to be Lewis and Clark in attempt to scuttle the Purchase.
Winston: There's one thing that's puzzled me from the very beginning.Hector: What's that, Winston?Winston: What is a pig in a poke?
- There are plenty of stories on the internet about stuff like this happening, either via eBay or Craigslist. It mostly revolves around either sporting games tickets (which can be worth hundreds depending on the game) or especially hot items (such as a tablet or video game console.) Thankfully if you're swindled like this eBay will normally pay you back what you paid to get the item.
- Sometimes the item in question is just the packaging that the hot item originally came in. Foolish people might try to pay for the item's full price, even though what's being sold is just the box or package it came in.
- In some cases, sellers are deliberately selling just the packaging (usually of rare or old games). Complete in box collections of classic games tend to be fairly rare (and expensive), and it's often cheaper to buy just the cartridge only, and get the packaging separately. And there are collectors who are specifically looking for just the packaging to complete their collection. Some people see the comparatively lower price for just the packaging and think it's the whole game without reading, even if the seller advertised the item correctly and didn't intend to scam anyone.