Update 9/10/2013: Earlier today, United Airlines published a mistake airfare and sold some flights for $5. According to reports, UA quickly shut down its online and telephone reservation system once the error was caught. So if you nabbed a cheap ticket, congrats. If not, don't worry, these things do happen occasionally and thanks to the magic of the Internet, we all hear about them pretty quickly. Unfortunately, so do the airlines. How do these things happen? And will the airline honor the ticket? Milepoint.com cofounder Gary Leff explains.

Original 11/15/2011: In the summer of 2002, Mexicana published a $55+tax business class fare to Puerto Vallarta, which made for a great getaway in the sun that coming winter. While I was laying on the beach, though, I wasn’t online and missed a British Airways fare of $20+tax for premium economy to most destinations in Europe. I’ve had an oceanfront two-bedroom villa with private pool in Khao Lak, Thailand, for $33 per night (including breakfast!), a $120 per night overwater bungalow in French Polynesia (including meals!), and $33+tax business class tickets to Cyprus with allowable stopovers in Italy.

These are usually known as mistake rates, error fares, or "fat finger discounts." The Alitalia error was supposed to be a discount $3,300 ticket, the last two zeros were left off. Other times they’ve been currency conversion mistakes, as with the overwater bungalow in Moorea (priced in Congolese Francs—CDF—rather than French Pacific Francs or CFP) or the Tokyo Hilton where an executive floor room was 300 Yen rather than 30,000 Yen (and thus three bucks a night).

Historically airlines—especially U.S. airlines—have been generous in honoring "obvious errors" whether they’re legally obliged to or not. United was famous for a $28 fare to Paris, or more recently an $1,100 business class roundtrip to New Zealand (upgradable to first class!). But they do not always honor, or fully honor these rates. Two years ago British Airways published a cheap fare to India, $40 + taxes and fees. They quickly cancelled the tickets, and the Department of Transportation insisted that they make travelers whole for any expenses that had been incurred for other non-refundable travel in the meantime. BA actually lost a small claims case related to the fare, and settled another one. According to the Wall Street Journal, United, Continental, Southwest, JetBlue, and Singapore Airlines all say their policy is not to cancel tickets when a mistake is uncovered, no matter how big a mistake. American Airlines says that they take it case-by-case. Korean Airlines, on the other hand, recently cancelled tickets a full two months after they had been booked. At the beginning of September, tickets to Palau via Seoul were available for less than $500. Within the past two weeks they’ve been contacting customers to let them know that because the fare was a mistake, they will not be honoring the tickets.

I’ve always felt that a mistake is a mistake, if it’s handled appropriately—contact customers quickly, cover actual losses that customers incur because of the mistake—then it’s at the airline’s discretion to decline to honor fat finger fares.

I’m happy to book them, because sometimes that airline or hotel will decide to honor them, and if they do I want to be in for the experience. But I won’t complain when they do not.

My usual advice is just to wait a few days after booking an obvious mistake, to see what the travel provider chooses to do, before making additional prepaid or non-cancellable arrangements. In the case of Korean, that advice wouldn’t have been enough since they waited two full months to contact customers and cancel tickets. And at almost $500 per person, it’s not the same sort of deal as $33 for business class to Cyprus. Which is why I believe Korean has handled things very badly.

For more discussion of mistake fares, visit the ‘travel hacking’ forum on MIlepoint.com.