just go to your local college and ask a few people where they sell their books at, at the end of the semester. you more than likely wont ask more than 4-6 people before you get an answer.
because most people sell their books.
most colleges have a place real close by (the closer, the better) that buys books from you and sells them as well.
in most cases youll get half of what your books worth even less if its in bad conidition
that same place actually sets up shop during the last few weeks of a semester and buys books out on the quad..i dunno how they do it out there though, but thats how it is here.