a pig in a poke something that is bought or accepted without knowing its value or seeing it first.
☞ In this expression, a poke is a small sack or bag, a sense which is now found chiefly in Scottish use.
2012The Age (Melbourne) Is that what we will get with Abbott? No one knows; yet it seems Australians are preparing to buy a pig in a poke if and when they get offered the chance.