Origin of Phrases - P
Pig in a poke
Meaning: An offering that is foolishly accepted without being looked at first.
Example: I bought a used pickup truck, but it turned out to be a pig in poke because it burned oil.
Origin: A poke is defined as a bag or a pouch and is the origin of the word pocket - a small pouch.
At medieval markets, unscrupulous traders would display a pig for sale. However, the pig was always given to the customer in a bag, with strict instructions not to open the bag until they were some way away. The trader would hand the customer a bag containing something that wriggled, and it was only later that the buyer would find he'd been conned when he opened the bag to reveal that it contained a cat, not a pig.
The phrase refers to the failure to look inside the bag or poke.
See the related phrase "let the cat out of the bag".