I can only speak for my local library and area. A twice per year sale of books no longer wanted on the shelves of the local library is the main mechanism for raising funds for our Friends of the Library organization. It costs the library nothing as we just use the large multi-use room on the top floor and the cashiers tables are manned by volunteers. We also take in books donated by individuals in the community. We gladly accept anything that is in good enough shape that it does not belong in a paper recycle bin, except no textbooks. Set prices are cheap, $0.10 for paperbacks and $1.00 for hardcover, and we generally sell out everything.

Those Cracked.com articles tend to be a germ of truth with a whole lot of exaggeration and humor thrown in.