Interesting story:
http://www.frequentflier.com/blog/ab...t-flyer-miles/
Basically, United fucked up and accidentally offered a trip to Hong Kong for 4 miles (worth about 12 cents) plus a $40 processing fee.
Upon realizing what they did, United contacted the purchasers and told them that the offer was retroactively canceled, and their money/miles were being refunded.
People got pissed and filed a complaint with the Dept of Transportation, who ruled for the airline.
I am usually hard on companies when they do shit like this, but I'm actually on United's side on this one.
It's one thing when a company offers a misleading promotion and then doesn't want to pay out what people thought they were getting, but this was clearly a mistake.
I don't fault fliers for trying to take advantage of this, but they also have to accept the fact that United caught the mistake and fixed it within a very short time. (It's not like they canceled people's flights the day they were flying!)
The law varies on this from state to state, but generally the law states that egregious, obvious mistakes on special offers are NOT the responsibility of the company to cover, unless it appears to be intentional or reasonable. By "reasonable", I mean that it's something that the average consumer could legitimately believe is a real offer, rather than an obvious mistake.