system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it legal for teachers to make money from requiring a student to buy a book that they wrote themselves? Isn't this a conflict of interest?
gpt
It might be a conflict of interest but it isn't by nature.

If the school and professor came up with an idea for a class and there was no suitable material for that class and so the professor wrote one - then shouldn't they be entitled to fair compensation (which is a whole different conversation)?

If it is a general subject and there is a lot of other material out there or if the price of the professor's book is grossly out of proportion then it may be a conflict of interest.