I remember my school had used some automated grading tool provided by the textbook publisher for differential equations. The nasty thing about it was you could

I remember my school had used some automated grading tool provided by the textbook publisher for differential equations. The nasty thing about it was you could pay an exorbitant amount of money just to access the homework site (you were required to buy in because it was part of the grade), and for a little bit more money it would include access to the electronic textbook for the duration of the course. And new textbooks included one-time vouchers (and of course the used textbooks didn't come with any voucher). Given the cost of the voucher, you might as well just buy the new textbook every time. Unfortunately, the textbook author was also the instructor of the course who claimed not to have received any benefit from this arrangement.