I've been to lots of used and/or small indie bookstores and service varies from store to store. And when it's bad, it tends to be horrid.
Recently I was dropping off a few books at a used bookstore. Among them were some ex-library books, bought from public libraries selling off tomes that hadn't been checked out in years, decades even. Others were bought at used bookstores years before. I've brought old former library books into shops before to sell with no problem. I don't see why it should be a problem. (Edit: And to clarify, they were all marked as discards and such one way or another)
I took these books out, about a dozen old paperbacks, some of them ex-library copies and a few ex-library copy hardcovers and the next thing I know the clerk behind the counter is staring, scowling even at the ex-library books.
"What are you trying to do here?", he snapped at me.
Bewildered, I said "What?"
The next thing I know, I'm getting a nagging lecture about how dare I try to turn in withdrawn library books, blah blah blah, it's so unethical blah blah blah and I can't get a word in edgewise at first, then I try to explain these are former library copies but he won't hear a word of it. The manager comes over and I end up wasting 5 or so minutes trying to convince this guy I'm not trying to fob off stolen library books on them. So I do end up selling the books anyways, and I leave the store in a huff. It just galled me that such a simple transaction ended up being such a hassle. The worst part was the prissy condescension coming from the clerk, twittering on and on and lecturing me like a toddler caught with his hand in a cookie jar.