So you take a deep breath and with one very loud-seeming click you buy your plane ticket.

But then the unthinkable happens – you see a lower fare elsewhere. Or the price of your ticket drops. Now what?

If your fare drops within 24 hours, your airline might refund the difference.

Several airlines offer a low-fare guarantee: If within 24 hours after booking a fare through an airline’s Web site you see your flight advertised for less on another site, your airline may refund the difference and also reward you with a travel voucher. However, that lower fare needs to meet precise conditions. On American and United, the lower fare must match your original fare’s itinerary, cabin (economy, business, or first) and class, a designation for differently-priced groups of seats within a cabin, usually indicated with a capital letter on your itinerary.

Class is often the hardest of the criteria to match, given that there can be a dozen or more of them within a single cabin. For Continental and Northwest, the lower fare must match your original’s cabin, itinerary and flight (two different flights can have the same itinerary if they share the same flight date and flight number, according to Northwest), while to Delta, flight is just one aspect of what they define as your itinerary. If you book your ticket through Orbitz you’re potentially eligible for a voucher through their low-fare guarantee if you find a lower fare on another Web site; you might also nab a cash credit through their price assurance policy if another Orbitz customer books your itinerary at a lower price. But, as with the airlines, the class and the other parameters for the two tickets must align exactly.

If the price drops after day one, you might get a voucher.

If you purchased your ticket directly through your airline and the price drops, the airline will issue you a voucher for the difference toward your next ticket. However, you will only get the voucher if the amount of the price drop exceeds whatever rebooking fee the airline might impose. For instance, my colleague’s wife bought a ticket to San Francisco for $339 that has since dropped to $319. But since the rebooking fee on her airline is $150, her fare needs to drop below $189 (her original $339 minus the $150) before she sees a dime of her voucher. If you want to get in the business of chasing vouchers and catching them, call your airline before you book to see if they have a rebooking fee (the flight tracking site Yapta maintains a chart of rebooking fees at major airlines) and book your ticket as far in advance as possible.

If you stick with it, you might get more than one voucher.

Like Farecast and several online travel agencies, Yapta searches for the best fares for you to book. But for the voucher-minded, Yapta only returns fares that can be booked directly with the airline (airlines won’t grant vouchers for tickets purchased through online travel agencies like Expedia, Travelocity, or Orbitz). After you buy your ticket, Yapta monitors your fare and e-mails you when it rises or drops.

If your fare drops to the point where you qualify for a voucher and you don’t want to deal with the airline yourself, Yapta will do it for you for a $15 fee per service action (if there are up to five people on your reservation, Yapta will get you voucher money for each ticket in the reservation for the flat fee). Once you give them the go-ahead, “we call right away in case the fare goes back up,” says Tom Romary, CEO and co-founder of Yapta. And since the average ticket goes through 21 price changes over a 45-day period, there’s a good chance that fare will shoot back up again. But if it falls even further than the point that yielded your first voucher, you could be eligible for more vouchers, right up until the time of your departure. Amy Terrell, program manager for Yapta customer service, said on one particular ticket she called three times over a six week period and got money back each time.

If you keep calling you might get the answer you want.

“What we’re finding is 80% of people tend to call [for the vouchers] themselves, and it takes about 15 minutes, Romary says. Terrell concurred that many of the calls she makes on behalf of customers are short and sweet, but as always, that can depend on who picks up the phone. “After booking, if you’re eligible for a voucher, don’t take no for a first answer. One thing you hear [from airline agents] is that ‘it’s not that price anymore’ – but it is – and sometimes they have to look in their system. Or they’ll tell you it’ll cost to rebook, even though their policy states that it won’t. Sometimes you get an agent who doesn’t quite understand what you’re asking or has been trained differently. Sometimes we make 3 or 4 calls [for one voucher], but that’s on the high end.”

Aside from being persistent, Terrell says that when trying to extract your voucher from an airline agent, avoid using the word “change,” which connotes you’re changing the date, time or name on your ticket and has a hefty “change fee” attached to it; all you’re doing is rebooking your ticket at the lower available price, and paying a rebooking fee if there is one. Also, avoid using the word “credit.” While some airlines use the words “credit” and “voucher” interchangeably to refer to your post-booking refund, “credit” harks back to trying to credit your original form of payment, which the agents will quickly tell you can’t be done. Stick to saying “voucher” over and over and if you keep at it, you just might get one. Or two.

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