Disposing of text books presents problems, depending of course upon the subjet matter.
Stuff like out-of-date computer technology is never likely to regain value.
My daughter had to clear out her school's History Dept book stock fairly recently and was aggreived that no mechanism existed for selling on these wonderful old texts which were currently out of fashion but nevertheless were eminently collectable. Quite a lot of them, rather than end up in skips, found their way either onto her bookshelves, those of her colleagues or in her loft.