My library has twice yearly book sales, and limited storage space. Books are collected the week prior to the sale, then sorted. Currently the library is purging lots of books that are put in the sale also. There are always books left over, and for years we had a book dealer come to take them. Now we send them the Better World Books, they pay the shipping costs. When any of them sell, we are periodically sent a check. It adds up, and we do get some return for them. Their website says they deal with thousands of libraries.