It's no secret that textbooks are expensive so I've found it really helpful to be able to sell back/trade in textbooks and make a bit of money back.
As an English major, my books aren't too expensive - but instead I typically need a lot more books per quarter than say, an Econ major. For each of my English classes, we read on average 3-5 novels a course, so with all my courses that sometimes adds up to 15 or so books a quarter! Even though they aren't too pricey, I always do make an effort to sell them back in order to make a decent turn around with how much I spent on them originally. There are many websites/places that are willing to take back used textbooks so I put together a little guide on where you might want to start looking.
Chegg.com - is a mostly known as a website where students can rent books for the quarter and just return them with free delivery. The concept is pretty cool concept: you just type in the ISBN number of the book you need, it pulls the book up and you can purchase it. However, they are also willing to buy books back, even if you didn't originally purchase them from the site. At the bottom of the page there is a link titled Sell Textbooks where you can type in the ISBN number and check what the rate they are willing to buy from you is. Also, it's free shipping both ways so it maximizes your profit in the end!
Amazon - Amazon is also a great resource that almost goes without saying. All you need to do here is create a sellers account and check to see what the book you are selling is going for in the marketplace. When I've sold books on Amazon, I've always made mine the least expensive one offered so it always gets sold right away. I've made a great profit from selling my books on Amazon and it's so easy, quick and efficient.
DePaul - DePaul's book store is the easiest and most obvious place to return a used textbook, especially if you bought them from DePaul to begin with. During the end of the quarter the bookstore is willing to check the condition of your book and the average rate for a buy back. You can do this in person or even online, so it's really easy and usually pretty profitable. I prefer this way because if you bought a book for a course offered by DePaul, the course will most likely be offered again the following quarter so students will need to purchase the same book...so usually there's a big demand for the book you're trying to return.
These are the three easiest/most efficient ways to make a bit of money back after shelling out a ton of cash for textbooks!