When Hilton (or any travel provider) accept a reservation, they make a committment. Period. End of story. No ifs, ands, or buts. If a confirmed reservation is not ALWAYS honored by a travel provider, then no one is safe. Ever.

Where is the line to be drawn?

Hotels HAVE in the past offered zero dollar/night rates as part of special promotions, or to attract attention. Should the burden be on the consumer to double and triple check it?

Yes, in this case, the 300 nights person is CLEARLY absuing the system, and I feel that he should be ashamed of himself. His intent was presumably to hold Hilton hostage over this. However, he didn't force Hilton to load a $0/night rate into the system. He requested it, and got a confirmation number. Doing so make him a bad person, but he is a bad person with a committment from Hilton for free rooms.