One of the other losses with the diminished or nonexistent secondary market for used textbooks, is the option for students to find alternative teaching approaches that work better for them.
I was shocked and chagrined when I got to grad school to find that many of the other students made a habit of having two or three different reference textbooks for any difficult course. No one had ever suggested this to me as an undergraduate.
So, when I was teaching, I put that idea out there and relied on it myself.
The department-determined intermediate book was one of three options of equivalent overall quality but very different style.
It was as much a barrier to some students as an advantage to others.
And the so called official ‘Study Guide’ prepared by a different set of authors seemed to come from a yet different way of thought and was riddled with errors in its answer key. More of a trap for the unwary than a help.
So, I would frequently use explanations and examples from the competing texts when they were clear and helpful to give a different entry point into material that students didn’t find intuitive.
I always identified the alternative texts on my syllabus at the beginning of the year and encouraged students to check out used books or library reference copies of the other books to see if those explanations worked better for them.