Does any author make money from having their own students buy the textbook? All the authors I know get no royalties from copies sold at their own Uni, to avoid the appearance of conflict of interest.
Technically, you are correct. I've heard of shadowy ways around this, like, "Hey, colleague at other school! I'll adopt your book if you adopt mine."
Eww!
I wish I had something more profound to write but that hits my thoughts about that kind of trade.
Alan