When you hear someone talk about buying a pig in a poke, they aren’t talking about real pigs. It’s a comment made to indicate that a deal has been foolishly accepted without having done due diligence to confirm that the deal is what it is purported to be. At the end of the day, a pig in a poke is a blind bargain, and usually it’s not much of a bargain for the person buying it.
So how did buying a pig in a poke come to mean this?
Back in the 1500s, a poke was the word for a cloth sack, and merchants sold piglets in these pokes, almost always sight unseen.
IMPORTANT SIDE NOTE 1: The word poke comes from the French word poque, and as is the case with many French words, when the item is smaller than average, ette or et is added to the word. The word pocket came about this way, and originally it meant a small bag.
IMPORTANT SIDE NOTE 2: This expression, contrary to popular belief, is not responsible for the idiom to let the cat out of the bag. After all, sight unseen, a cat in a bag would not be mistaken for a piglet in a sack. Additionally, the idiom to let the cat out of the bag only began to appear in the 18th century and if the two expressions were linked in some way, they would both appear within a few years of each other.
IMPORTANT SIDE NOTE 3: While the two idioms mentioned in #2 are not related, it is important to note that the French do indeed use the expression acheter un chat en poche when talking about a bad deal, and it is from that expression that many mistakenly believe letting the cat out of the bag is an extension of buying a pig in a poke.
In 1530, London grocer Richard Hilles published his book titled “Common-place Book” in which he gave the following advice:
When ye proffer the pigge, open the poke.
But that advice was gleaned from a poem titled “The Proverbs of Hendyng” published in 1275 which warned:
Wan man ȝevit þe a pig, opin þe powch.
[When a man gives thee a pig, open the pouch.]
This concept is the basis for the warning caveat emptor — let the buyer beware — in commercial law.
Idiomation was unable to trace the idiom back before 1275, however, it is a very sound piece of advice and because it is, it is likely the spirit of the expression dates backs several hundred years earlier even without being published elsewhere.
Historically Speaking 