The lending period cannot be extended. A book can only be loaned once for a period of 14 days, and only if lending is enabled by the publisher. Amazon also has some pretty strict guidelines for profiting off something like this. I'd be far more worried about them than Listia... Although no money is exchanged, there is a lot more emphasis on copyright protection than ever before. I'd proceed with caution. Personally, it's not worth the gamble. Since you can't even give your books along with your device if you transfer ownership to someone else, I'm pretty sure they'd have issues with auctioning off the right to borrow a Kindle book.