While there are quite a few companies in the textbook rental and marketplace space, this seems to be the only one doing flat-fee swaps: http://edubookswap.com/
Yes, that would pose a problem for my idea, but do you think Lendsit would be able to compete since it's completely user-based? It would be more of a platform/forum where students could just type in the book they wanted and check to see if we had it.
Thanks for the response! Alex