That's true of books and thrift stores in general. Every year, before the start of school, I go to Goodwill with $30, and buy children's books for my classroom.
When I was a kid, we got free books from our neighbor who worked at the local publisher (printing facility). They were the not-quite-good-enough-to-be-sold books (although we could never find any flaws), and had "reject" stamped inside the front cover. I always wondered what that did for my self esteem.