One day soon, downloadable digital textbooks will eclipse paperbound textbooks. It's simple arithmetic. It costs more to print, warehouse, ship and sell paper textbooks; digital copies will be instantly available from the publisher at lower price, they will never get outdated or go out of print, and there will be no recycling, no secondary market for us booksellers to profit from.
College students and homeschooled students will simply download to an e-reader, a tablet computer, perhaps a device that isn't even on the drawing boards yet, and we'll all have to say goodbye to secondhand college textbook sales. It was good while it lasted.
It's time to take action.
If you stock textbooks for sale (I still carry a few of them), be prepared for the day when they could be obsolete. I would make plans now to clear out old used college textbooks. Now is the time of summer they are selling. Discount them. Sell them just above cost. Free up your inventory bookshelves, and be ready to concentrate more on non-fiction titles that are rare or hard to find.
If you have progressed to selling your used books and other media on Fulfilled By Amazon (FBA), then it's time to start the clearance sale there as well. There will be fees to be paid on slow moving inventory you'll be taking up in their massive distribution centers. Get rid of those textbooks now while they still have some value.
Doing this now will save you the anger of having to throw away those textbooks in the trash in a couple years.
Here's a link to Google Play, offering up to 80% off textbook pricing: https://play.google.com/store/books/collection/promotion_1000568_txb_product