Alex Tabarrok points to a discussion of a travel website that appears to price the same hotel differently depending on how results are sorted — offering lower prices for the same room if a person search the site chooses to sort by price (presumably indicating that price is their key criteria for choosing a hotel).
I’m not sure I’ve ever seen results precisely the same, but I do understand that Hotwire has been known to offer slightly different pricing to users of different web browsers (perhaps the theory being that more obscure browsers indicate net-savvy individuals who would be more price sensitive?). And there’s a current Flyertalk discussion on whether the ever-problematic USAirways website prices flights higher for Dividend Miles members that are logged into their accounts (although I suspect that it’s a preferences issue for the member reporting the phenomenon).