Buy from "friends of the library" organizations. Most library branches have a "friends" organization which raises money for the library by selling used books. These books are usually in good quality and well priced. Take advantage by finding the "friends of the library" organization in your area or by visiting your local branch.
Buy book lots. Many large-scale book sellers sell book lots that come from libraries. These book merchants buy and sell a group of books, called a "lot," which contains hundreds and even thousands of titles that once sat on library shelves. Contact dealers through book seller websites like Biblio.com to find a seller.
Shop discount retailers. A number of discount book retailers sell library books that are still in good or very good condition. These books are often popular titles that were overstocked in the library or saw a slide in demand over the years but are still great books.
Look on used book websites. Even mega-commercial sites like Amazon.com serve as an outlet for the sale of library books. Like other outlets for library stock, these books are generally well cared-for and in good condition. Search networks like Amazon or Powell's to find these books.