The other difference, I think, betweenthe $29 United flights to Paris and the $0 Hilton reservations is that in the case of the United flights, United made the offer and collected payment for it: the people who booked on the website did not just make a reservation, they bought a ticket, gave UA their credit card information, and were promptly charged for the ticket. UA accepted their offer and their money.

The people who took up the Hilton reservation offer didn't pay anything.

Also, though it's not strictly a legal point, they shoulda known better. Cheap is promotional; free is a mistake.

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"Yes, but at least mine will be found in a first class seat." -- Peattie and Taylor