There is an enormous market in pre-owned college books. It is organized formally through bookshops and websites, and informally through college notice boards. Students will usually be able to buy the books they need at far below their new cost, once they start their course.

Bookshops and online bookshops will buy textbooks at the end of the year for a pittance, because there are no buyers in the market at that time. These companies hold onto the books for 2 months, and then sell them for the new, higher market price at the beginning of the new college year. The market price in September is much higher because now, there are more book buyers than book sellers in the market.

If you are selling last year's books the best way to get most of your money back is to hang onto them until the new college year starts, then advertise them on campus, or use EBay or Amazon to sell them.

If you want to buy your next year's books for the best price then ask around, even advertise on campus, or throw a website together and buy them in May or June, not September. You could even make a business of this. You could borrow money to buy hundreds of books in early summer, buying your stock for next to nothing. You then sell your stock in the fall, realize your profit, pay off the loan, and still have enough to buy books next May without borrowing.

You need to do your research with the faculties to find out which courses are changing significantly, which ones are expanding numbers and which courses will be taking on less students next year.