Make sure you are getting the right textbook edition. You need more than the title and author from your college professor - get the ISBN to be sure you are getting the right edition.
New books come with supplemental materials, online codes, CDs, or DVDs - keep this in mind when buying a used textbook or getting a textbook rental.
If you decide renting will get you the best cheap textbook, remember to not incure additional expenses by returning the book by the due date, and in good condition.
If you rent books you don't have to worry about selling back your books, but if you buy secondhand textbooks make sure you sell back books .