Have you ever received a voucher as compensation for an unpleasant travel experience or for volunteering to take a later flight? If so, make sure to understand how the voucher may be used and with which fares — all vouchers are not created equal!

Case in point: The other day, after researching the fares online first, I called US Airways to redeem a $100 voucher. The agent was able to find the exact fare and itinerary I wanted, but after 30 minutes of trying, was unable to apply the voucher. Reason? The fare in question was a “web only fare.” The voucher could only be applied to a fare that cost $168 more! By my calculations, the privilege of using the voucher would end up costing me an additional $68. I said thanks, but no thanks, and took my business elsewhere.

(Incidentally, the jury is still out on this one, because the terms and conditions read, “May be used toward the price of one ticket/one fare on US Airways, US Airways Shuttle, and US Airways Express, as well as their codeshare partners.” I can’t find the limitations.)

The moral of this story — Each airline offers a variety of vouchers for free round trips or dollars off a paid ticket. Make sure you understand the terms and conditions before you agree to a voucher or try to redeem it. My experience is that free round trip vouchers are difficult to use, because they book into an award ticket class where there are fewer available seats. Dollars off vouchers are more easily redeemed, either online or by telephone, depending on the carrier’s policies.

Check the airline’s different airfares first. Check airfares on competing airlines. That is the only way to know the real value of your voucher should the reservation agent tell you it only applies to select tickets. If vouchers are not used correctly, they end up costing more money or being as worthless as the paper on which they are printed.

Final note (and a caution): Airline vouchers all have a value, however, they must be used correctly. Vouchers are also, often, transferable — other passengers can use your voucher. There is an active voucher market on E-Bay and I have heard of friends and co-workers who pass vouchers around occasionally. However, be careful. In the voucher market, scams are notorious. It is best to only use vouchers from friends or business associates who may not be able to use them.