There is a huge amount of pent-up demand there.
Take the extreme but famous example of when one of those books, Lisp in Small Pieces, was mispriced for $13 including shipping at amazon.ca in 2007 -- it became the #1 seller, on a book that I imagine sells maybe a thousand copies in a year.
Nobody actually got their book (the publisher probably didn't have that many) and $13 is ridiculously cheap, but it's a fascinating story. Clearly, a lot of people had that book on their "someday wishlist" (a fantastic market for deal sites) or just appreciate a seemingly one-time deal on that kind of item.
If you can package books together, app-bundle style, or sell them out of season with the academic calendar, it would offer a good opportunity for price discrimination.
Also, although academic publishers are super-wary about the used book market, they also know that their textbooks are being torrented left and right. Maybe this would be a channel they could have more control in.