The best time to sell your used books is during finals week, at the end of a term. That means the bookstore can pay more for your used books. The bookstore staff wants to buy current edition books that your professors have ordered for use next semester. If you have a current edition textbook that is not in use on the Utica College campus next term or which the bookstore has met its demand for, the staff checks the national market price for the books. The price the national market will pay you for your book is much lower.
Publishers issue new editions of textbooks frequently.
When a new edition of a title comes out, the previous edition loses its value and, unfortunately, the bookstore cannot buy them. You may wish to keep these books for your own library, since they can still serve as valuable reference, or you may wish to donate them to a charity.