to buy, get etc sth. without having seen it, without having carefully examined its quality
X купил кота в мешке ' X bought a pig in a poke
X bought thing Y sight unseen, о КОТ В МЕШКЕ
NP
sing only) ' a pig in a poke.
«Гляну пойду для порядка на животину твою. Потом и порешим. А то вроде как кота в мешке обговариваю» (Максимов 3). "I'll go and take a look at your animals (sic), just to do things properly. Then we'll decide. I won't want to buy a pig in a poke"(3a)
Loan translation of the French acheter chat en poche.
Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. С.И. Лубенская. 2004.