I noticed that Amazon.com has started up their own Textbook Buyback Program as the school year comes to an end. I should have also tried Amazon back when I was getting rid of some old textbooks earlier this year. I just ended up selling to whomever offered me the most dough. Check out my SellBackYourTextBook.com review and ValoreBooks.com review. If you end up using Chegg.com, you can get an additional $5 back with the promotional code CC125998.
Just type in your ISBN numbers into the BigWords.com comparison engine and see what they’ll offer you. Amazon seems to have the same buyback system, where you print out a pre-paid mailing label, send it back, and get paid. The main differences are that they offer free UPS shipping (some places only offer USPS Media Mail), and they only pay you back in Amazon.com gift certificates and not cash.