While the price of used romance novels and biographies isn’t high, the resell value of college textbooks can be significant. If you have some textbooks at home, you may be sitting on a gold mine of educational tomes. Simply enter the ISBN number (it’s inside the book on the copyright page) on the website cash4books.net. The site will list the value it's willing to pay for the book. Once you compile the books you want to sell, the site generates a free shipping label, and in a few days, you’ll get a check or PayPal payment for the value of your old textbooks.