When I was in college the problem of textbook purchases loomed over every students head at the beginning of every term. With the list of new classes came the list of new books to buy. I found the best time to sell my old books was right around the time people were selecting their classes for their next term. I would post my list of books and whose class they were for and anyone selecting those classes could purchase them. Another really good time to sell the old books are right at the start of term when the people who have not thought about their new textbook purchases are now in need of the book.