I found a real score recently @ a thrift store. It was in a large clear bag so I saw many of the fabrics. It was taped shut to discourage buyers from picking through the fabric. I bought it & told store clerk. "I'll just re-donate what I cannot use" - works for me. Often, there is no fabric worth buying, so I didn't mind getting some pieces I will give back for them to sell.
I should be more discriminating - my stash is getting out of hand.