Bargaining, and the law of one price on the internet: Axiomatic Models of Bargaining

Sometimes price variation on the internet is explained by search costs, etc., but below is an example that is hard to explain that way, since all the options are on the same page (e.g. who would rent a book for more than its purchase price?)  The example below is for my book, Axiomatic Models of Bargaining, which is available for free here (although just in pdf, not in the collectors' edition, which you can buy from Springer for $69.95).