At the end of the quarter at UC Davis, many students are left with textbooks they neither want nor need (or even opened). Bookstores often offer to buy back books so they can resell them, often for very low prices.
As an alternative, hold onto your unwanted books and go to the first session of the class the text is for and offer to sell your book. You can sell your book for more than the bookstores will pay and the buyer can get the book cheaper than at the book store. Everyone wins!
Also, you can try the ASUCD Book Exchange.
You can also post a flier on the bulletin boards of the building where that specific class is held - during the first few days of school. A generic "junk mail" type of e-mail account works well for that purpose, to communicate with potential buyers. For your safety, offer to do the transaction at a public place.