And why not? It happens all the time!! Students sell books, materials.
The tests are another story. That's where the trouble lies.
Has to do with distributing actual lectures for money, though tests would be far worse.
I don't think there is an issue if during a lecture 25 students report the teacher started to throw darts at a picture of President Bush and then urinated on our flag.
They can still report what needs to be I think.