blind bargain

Poke, pōk, n. a bag: a pouch.—A pig in a poke, a blind bargain, as of a pig bought without being seen.

From Chambers's Twentieth Century Dictionary (part 3 of 4: N-R) by Various

If I get paradise when my time comes, I can't help myself; but I'll venture nothing before-hand, upon a blind bargain.

From The works of John Dryden, now first collected in eighteen volumes. Volume 07 by Sir Walter Scott

And for once I'll make a blind bargain with you.

From The works of John Dryden, now first collected in eighteen volumes. Volume 02 by Sir Walter Scott

But he’ll strike a blind bargain in there.

From Pemrose Lorry, Camp Fire Girl by Isabel Katherine Hornibrook

Although Murray considered it "a blind bargain," he was disposed to accept it, as it might lead to something better.

From A Publisher and His Friends Memoir and Correspondence of John Murray; with an Account of the Origin and Progress of the House, 1768-1843 by Samuel Smiles