"to buy something without consideration".Follow the link, it may be helpful http://www.51voa.com/Voa_English_Learning/Learn_A_Word_22990.html?UpdatedPage=aGlqYWNr

The English colloquialisms such as turn out to be a pig in a poke or buy a pig in a poke mean that something is sold or bought without the buyer knowing its true nature or value, especially when buying without inspecting the item beforehand. The phrase can also be applied to accepting an idea or plan without a full understanding of its basis. Similar expressions exist in other European languages, most of them referring to the purchase of a cat in a bag. https://en.m.wikipedia.org/wiki/Pig_in_a_poke