I'm helping a friend out at a 2nd hand bookstore. People bring us books and sometimes we go hunting for them at estate sales and Friends of the Library sales. We're mainly looking for classic and recent paperbacks since we've found that our customers are reluctant to buy hard covers even when they're about the same price as paperbacks.
We have come up with some interesting finds: first edition signed books by Tom Robbins, Alan Furst, Margaret Millar and Sue Grafton (she was a local girl so they're a dime a dozen though we only have a couple from before ""H" is for whatever it's for..""). But we've found a lot of great old paperback by Ross MacDonald (another local), Chandler, Hammett etc. Also things we're enthusiastic about even if our customers aren't: Pynchon, Joyce etc. (Actually we do eventually sell most of them.)
But we're still looking for that elusive Ben Hur, 1860, Third Edition, the one with the duplicate line on page 116.