Wednesday’s $39 Alitalia business class fare from Toronto to Cyprus caused quite a buzz, but only a lucky few were able to grab it. Fewer still will see the ticket honored.

Instead of $39, the fare should have been $3900. Oops.

The Wall Street Journal reports (subscription) that 509 tickets will be honored, most purchased through Orbitz. Judging from the discussions here, many more people tried and failed to get the tickets. Only those customers who received confirmation of the purchase from both Orbitz and Alitalia will get to fly at that price. (Whether or not they’ll earn miles, that’s another story…)

This isn’t the first time this has happened. Travelocity and Air Pacific honored $50 tickets to Fiji, USAirways honored $2+tax cross country fares, and United honored its $20 fares from San Francisco to Paris. But not every booking agency or provider is as customer-friendly. The hotels, in particular, seem to renege on these offers more often than the airlines. Sure, some of these rates should never have been posted, but with Ryanair and Easyjet regularly selling seats for zero base fare plus taxes, or Spirit’s recent advertised $9 fares to the Caribbean, why shouldn’t the public assume some of these prices are legit?

Unfortunately, you just never know if the deal will be honored or not, but the corporate response will usually be swift. My advice is to book quickly, and ask questions later. Don’t call and ask for seat assignments or request a nonsmoking room, for example, until the dust has settled. Finally, don’t book non-refundable parts of the trip until you know the offer is being honored.

The hardest part is often finding out about the deal before it’s taken offline.

Enter the internet: Two websites in particular share a mission to alert travelers to these ludicrously low deals. Fare Alert sends e-mail alerts when someone reports a crazy-low fare sale to them. The tradeoff of an e-mail list is that the airlines themselves subscribe, so the mailing list tips off the providers that there is an error in their system. If you receive a FareAlert, act fast.

Free Traveling [Ed.: now defunct] offers much of the same thing, without the e-mail list, but with added attention to best-rate guarantees. So, for example, if TripRewards.com (the umbrella site for Cendant hotels) has hotel rooms at $75, and Travelocity has the same room for less, then you can book on TripRewards and invoke the best rate guarantee, making your room FREE. This is Free Traveling’s strength, but it’s often for limited dates and obscure locations. But hey, you might get lucky.