If you've never heard of Amazon's trade-in program, it allows you to trade in textbooks for an Amazon giftcard. If you use Amazon a lot (like I do), then it's equatable to cold cash (where you don't get as much of it). I use excel graphs to track the trade-in price and try and follow the demand trend. If the book is in high demand, the price will go up. One time, a book trade-in price was 110% percent of the original. The price of the book at purchase was 36.77. That's basically getting a refund and almost 4 extra dollars, just for waiting to trade it in (I didn't actually trade it in because I need it, but you get what I mean.) I am currently plotting the percent return every 4 days to see what I can get back.