Textbooks

[stardance]

I have a friend who is overly cynical about everything and it annoys me. Today he thinks that professors get kickbacks from textbooks, and so try to assign as many required texts as possible/ the most expensive texts possible. I think this is ridiculous.

So: Have any of you heard of a professor getting kickbacks from textbook sales?

and

Is this a common rumor among students? (For the record, this is the first time I've heard it).