Somewhat indirectly related question. Looking briefly at some websites, of which most of them look questionable, is there a site, other than amazon used books w

Somewhat indirectly related question. Looking briefly at some websites, of which most of them look questionable, is there a site, other than amazon used books where someone like myself could by old versions of college course books? Most sites look like they just buy books and do not have an outlet for the selling of books. For someone constantly reading about philosophy, it would be a nice change of pace for me to get some college related books that are not used anymore due to a new and "better" version being out.