I've seen similar things, with the reasoning being less "the university requires the professor to list at least one required text" (this one would be easy to si

I've seen similar things, with the reasoning being less "the university requires the professor to list at least one required text" (this one would be easy to sidestep: just require a cheap or free one and then use another) and more "the texts listed are required will be sold to students at a discount, so students can only profit from this... as long as they are in the know".