I once bought a Chemistry textbook for a summer class for $170, I went to sell it back to the bookstore a month later they wanted to pay $10 because a new edition was about to come out.
What makes me even more angry is that the new edition is 95% the same as the old one, except for the fact that they change the order of the exercises.
The textbook industry is just a big scam IMO. And if they scam me it's not that hard for me convince myself to scam them back too, specially when it's that easy, even when going against my moral principles.
Talking about textbooks only.