There is an interesting piece in today's Orange County Register about a math professor who is being disciplined by California State University Fullerton for failing to use a required (and very expensive) textbook-that was co-authored by his departmental chair
I will state here that as an adjunct teacher of English as a Second Language at UC Irvine, I use assigned textbooks. Like the CSUF case, my classes have multiple sections, which means the same class being is taught by other teachers in my office. There is a need for a certain amount of unity from class to class, so we don't choose our own texts. Were I to substitute my own texts, surely, there would be repercussions.
That said, I have an ethical problem with professors who assign their own texts for their classes. It is regularly done, I can assure you, but I still think it represents a clear conflict of interest. Same goes for a departmental chair who makes sure his or her books are required texts.
Full disclosure: I know for a fact that two of my own books, which I wrote several years ago, have been used as suggested reading by other professors at other universities-quite without my involvement. Are those books to be purchased in those university's book stores? Not to my knowledge although the UCI book store has offered my books for sale on the "UCI Authors" shelves. Mostly, however, my books are academic books by an academic publisher that markets to academic libraries.
Each academic subject has a multitude of quality texts that can be assigned to students. It seems to me there should be a university policy that no teacher-or departmental head- should be allowed to force their own books into the course and line their pockets in the process. A teacher can include his or her works on a syllabus as part of his or her bio. If the students want to seek out that book for further reading, it should be their choice.