Books that aren't being used at Navarro may be bought back by a wholesaler for the national market. Since the wholesaler has to ship books back to their warehouse, restock them and then resell them to other college stores, they naturally pay less than the bookstore does for the books that are staying on campus. The wholesaler determines the price they'll pay at buyback by tracking national demand for books and the publisher's revision cycles. We already have a gazillion of 'em in our store, so we can't use it here. It isn't needed here, but it's needed on other campuses.
Demand determines value.
The new edition is in, so the old edition is out. Your book looks like it's been through a tornado.