Buyback Estimate Type in the ISBN numbers found on the back of your textbooks and enter your e-mail address in the box provided. Our textbook staff will send a buyback quote for the total of your books within 2 business days. ISBN List: E-mail Address: E-mail is required in order to send you the buyback quote. This email will only be an estimate for what your books are worth at that time. Many factors can change the buyback price of a book such as class information, quantity bought back, time and condition.