Who'd be sued? The people who use booking.com with this extension? It'd be a genius (/s) move for a service to sue their customers, ensuring they'll never retur

Who'd be sued? The people who use booking.com with this extension? It'd be a genius (/s) move for a service to sue their customers, ensuring they'll never return. IANAL, but I imagine a sleazy lawyer from the company could attempt to sue the users for altering a "copyrighted work", although it probably doesn't apply if the derivative work isn't for public consumption. Also it would mean defacing a book would be illegal.