No, not book stores that have been used before, but stores that sell used books. I have a few hundred books, and I'm sure I could have spent thousands of dollars had I bought them all new.
I just picked up a decent paperback copy of The Rise and Fall of the Third Reich for pennies. I've also found two Korans (English translations), the complete Plutarch's Lives, Thucydides and Herodotus, an Oxford History of America, another American history survey by the Beards, Tocqueville and Madison's notes on the Constitutional Convention. And one by Bill Jordan and another by Elmer Keith.
I also like picking up books that I wouldn't want the publisher to profit from, like Arming America, and another book I have by Pete Shields.
I prefer used paperbacks to new hardcovers, most of the time. Used things sometimes have a certain character that seems to make them special...somehow. Can't explain it.