Like the other poster said, that's what libraries do when they're done with books. I help at my kid's school library, mostly shelving books, but also processing discards, which is remove from catalog, remove or mark over the barcode and library stamps so the book doesn't come back, then the librarian has to do some procedural junk and if nobody at the school wants the books, they get sold to a used book wholesaler and then hopefully to someone who wants it. The wholesalers don't pay much, but it helps buy new books the discarding has made room for.