When I was in college, at the end of each semester we’d go to the book store (you know, that place that fleeced us with $100 used books) and we’d sell back those books for about one tenth to one quarter what we bought them from. We’d then use that money to help fund one of our books for the next semester (or beer). Well, Amazon is doing something similar now. Although it has to do more with when new editions of the book are released. Each edition of a book allows you to trade the book in for new editions. Take Practical C++ Programming, from O’Reilly. Apparently I bought…