Their article, "The Quick Guide to Cheap Textbooks," offers both basic and specific ideas on how to buy used college textbooks online, like this selection from their article on their website, posted in early September 2014:
On a site like Amazon Marketplace, where you can see used book options from other sellers, evaluate the book’s condition and shipping times prior to purchase. To reduce shipping times, choose a seller that’s in your region. Students should also checkout the local, independent bookstores around campus, which often have stockpiles of used books from last year’s classes.
Here is the link to their article:
Amazon Marketplace has made it just a tad bit more difficult for us indie home-based booksellers to compete in the crowded arena of buying and reselling textbooks ... especially if their is an online access pass or a CD-ROM included in the original textbook that is now missing or not accessible because of prior use.
There is indeed money to be made in the textbook market. But be warned about new selling rules, and be advised that heavy college textbooks cost more to ship, especially if you opt to send the book in ways other than USPS Media Mail. Some sellers offer this option because the students need the textbook fast and classes are starting soon.