Amazon.com is a great place for selling your used and new books. If you are a student and trying to sell your used books online, you will notice the Amazon charges 15 % commission. That means for $100 book, Amazon keep $15. There is a cheap alternative called the textbooks.org. TheTextbooks.org charges only 6.5% commission.
TheTextbooks.org covers all campuses in United States. When you sell your book, select your own campus. Another student can contact your directly. You can choose to exchange book in person. There is no fee for that.