Once you finish school, old textbooks are often left to collect dust on your bookshelves. Instead of tossing these bulky (and expensive!) volumes, try selling them to Amazon. The company will buy back textbooks for up to 80 percent of the original price. Simply enter information about each textbook into an online form, and Amazon will give you its offered price. Print out a shipping label and send in the books to receive credit on your Amazon account. Learn more about Amazon's textbook trade-in program here.