I also managed a fairly large university bookstore and this is all very accurate. The bookstore that I managed was part of Barnes & Noble College Bookstores (related, but different from Barnes & Noble retail), and we were given a store discount on orders and would just apply a standard markup to all textbooks. Retail or trade books were just sold at whatever they were priced at.

We would always give the professors book order forms pre-filled with whatever texts they used the previous semester and most of the time they would just sign off on it. As long as the book was still available from the publisher, we could set a fairly high buyback target (where students would get the most money back) and it would be a pretty good deal for everyone involved.

The problem was when the publisher released a new edition between semesters. We couldn't order that book, and the buyback value would drop to almost nothing for the student. Sometimes the prof would just adopt both editions and tell the students to just use whichever one they could find, but if no professor is using a specific edition of a book for an upcoming semester, the resale value to a campus store would be a few dollars at best.

Anyway, get your books wherever you can find them cheapest, which is usually not the campus store. Also, try to encourage your professors to turn in their orders for next semester as soon as possible. The earlier the stores get the orders, the more cash you will be able to get back from the bookstore when the semester is over.