To buy something sight unseen (a “poke” is a bag): “The mail-order offer sounded like a bargain, but I didn't want to buy a pig in a poke.”
To accept or agree to something without careful examination; risk the unknown: It is unfair for anyone running for president ''to ask people to buy a pig in the poke''
Related Terms[1562+; fr dialect poke, ''bag, sack'']