Free Flights to Vegas, New York and Cancun?

Nov. 30, 2010— -- Matthew Klint might have just landed one of the best travel deals ever.

Next month, Klint, his brother and his uncle are all flying to Las Vegas and staying in two rooms at a five-star hotel. The total cost: $44. Throw in a $200 food and drink credit and they are actually making $156 off the trip.

How did Klint score such a deal? The 24-year-old Philadelphia law student saw a promotion -- possibly an error -- on Expedia's Canadian website and snagged it quickly.

Then he started booking other trips for friends and family. Ultimately, Klint purchased 15 tickets, most of them for free.

"I always recommend to people: book now and ask questions later," said Klint, who also has a blog about flying called Live and Let's Fly.

A few hours after Klint booked the tickets, Expedia caught the error and changed its promotion requiring all trips to start in Canada.

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Savvy travelers had caught on to a promotion where Expedia was offering $300 off any air and hotel package to Cancun, New York or Las Vegas. The deal was originally supposed to be just for Canadian travelers and aimed at longer vacations. But deal watchers saw it and word spread quickly on the Internet.

Besides his one-night Vegas trip, Klint is taking two mileage runs from his parents' house in Los Angeles to New York, just to get the frequent flier miles needed to re-qualify for elite status next year. The cost: completely free.

"This deal was so lucrative. There was no minimum stay," he said. "It just seems that Expedia dropped the ball and should have put a minimum night requirement."

Expedia declined several requests for an interview and only would say that it is honoring all bookings.

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Gary Leff, who runs the blog View From the Wing and re-posted the Expedia offer, said such deals come around from time to time but travelers need to act fast.

"They're usually human glitches, working with computers," Leff said. "They seem to happen every so often. But not as often as they used to."

While they might not be as frequent, thanks to social media and the Internet the number of travelers taking advantage of such deals seems to have grown.

Some favorites that Leff has taken advantage of have involved currency conversion issues.

Le Méridien Hotels in Thailand priced its rooms once in Ugandan shillings. Leff got a $1,500 a night, 3,100-square-foot presidential villa for 60 cents.

And there was a buy two nights, get the third free -- plus breakfast -- offer.

The hotel realized its mistake, but gave him the room for $50 a night, with the third one free.

When Hilton took over Starwood properties in French Polynesia, somebody improperly typed in the currency code. CFP, is the proper code for the franc in French Polynesia. But CDF -- the code entered into the reservation system -- is the official currency of the Democratic Republic of Congo. Rooms were being offered at only 10 percent of the price.

Airlines also make mistakes and tend to honor such errors.

"Hotels are more iffy," Leff said. "Sometimes, you win, sometimes you lose."

Most often, these deals come when something gets entered into a computer incorrectly, said Rick Seaney, CEO of airfare-search site FareCompare.com and an ABCNews.com columnist.

For instance, a couple of years ago, United was trying to match Southwest fares. By mistake, somebody set Southwest's one-way fares as United's roundtrip prices.

"So for a full part of the day, they were selling tickets at half price," Seaney said.

United quickly caught the error and fixed the fares but not before thousands of tickets were sold, all of which Seaney said the airline honored.

One New Year's Eve, Air Canada was switching over its Website and for a brief time was offering tickets for zero dollars.

"There's been a variety of things that occurred," Seaney said.

Perhaps the best deal of them all came from Italian airline Alitalia. Seaney recalls the airline was trying to offer unrestricted business class tickets from Toronto to Cyprus for $3,300. Thanks to a mistake, tickets were sold for $33.

But it gets better, the tickets allowed long layovers. Some savvy travelers got to fly business class to Rome or Milan on the way to or from Cyprus.

Alitalia started canceling the tickets but then people complained to Orbitz, where they bought the tickets. The airline started re-booking tickets but messed up the tickets so much that they had to allow one free change for everybody.

Delta once forgot to add the fuel surcharge on round trip fares, Seaney said, making roundtrip travel to Europe extremely cheap.

Airlines realize the problems pretty quickly and try to fix it as soon as they can. With domestic airfare, the prices can only be changed in computers three times daily.

"If they have a problem at 8 p.m., they can't fix it until 10 a.m. the next morning," Seaney said. It's even better for travelers on weekends, when the domestic prices only update once, 5 p.m. ET. International fares can be updated hourly.

To take advantage of the deals, follow blogs like Leff's or the popular FlyerTalk forum, where these deals are often found in the mileage run section. Seaney also suggests keeping track of Twitter feeds.

Several travel sites offer nightly or weekly deal alerts, but Seaney said as soon as his computer system at FareCompare.com identifies an anomaly, it automatically emails out an alert to subscribers.

"In order to take advantage of mistakes," he said, "it has to be in real time because they are fleeting."