I got 2 books this way from a book store and they were lightly used books that employees had donated and all the money was being donated to a charity, which I think is a good way to do it.

They're all only $2 or $3 so even if it ends up being one you've already read it's not such a big deal, and you know your money is going to a good cause. And since they're books the employees owned, you know they're probably good!