Sometimes, those airline vouchers are like a lump of coal

Many of these strandees will garner goodies for their troubles: airline vouchers for free seats, hotels, meals and more.

Tidings of joy.

But you'd better watch out for the fine print. Otherwise you'd better not pout if you don't get what you want.

"I'm not saying vouchers are bad," said Terry Trippler, a Minneapolis-based airline expert with http://www.cheapseats.com . "But they're not gold."

That's because vouchers nearly always carry restrictions.

You may have to redeem flight coupons in person or by phone, incurring a fee. Or they may be good only for certain fares or categories of seats. They may expire after a year. A hotel may refuse to accept a voucher or, especially during weather delays, run out of rooms.

"Vouchers often aren't worth what they seem at first glance," said Edward Hasbrouck, the author of "The Practical Nomad" books who works with Airtreks .com, a San Francisco-based travel agency.

You may be better off bargaining for cash, experts say — if you can get it.

And bargain you will, under a curiously unregulated free-for-all bidding that airlines employ to entice you to relinquish your seat on overbooked flights. Negotiating for a hotel or meal voucher if your flight is delayed by weather or other causes — not a given — is equally unregulated.

"There are no ground rules," Trippler said.

Except for one situation: getting bumped against your will from an overbooked flight.

Depending on how long you're delayed, the airline, under federal rules, may owe you up to $400 if you're denied boarding on an oversold domestic flight or certain international flights, plus it must let you use your ticket on another flight or get a refund. (For details and exceptions — as with all regulations, there are many — go to airconsumer.ost.dot.gov/pubs.htm, and under "Other Publications" click on "Fly Rights.")

The U.S. Department of Transportation also requires that before bumping anyone involuntarily, a carrier must try to get volunteers to give up their seats. But the DOT doesn't say what type of compensation must be offered.

These days, it's likely to be a flight coupon.

"They're going to offer a voucher first because they don't want to give you a check," Trippler said.

He and Hasbrouck agreed that it's usually better to go for the cash than the ticket voucher because at least you have something in hand. Don't expect to get more than $400 on a domestic flight, though, because that's the most the airline may owe a bumped passenger under DOT rules.

Beyond that, it's all negotiable. Seats on long or infrequent flights may be worth more. Hasbrouck said he once saw a passenger awarded $300 plus a hotel voucher plus a business-class seat for being bumped from a flight from Kuala Lumpur, Malaysia, to Los Angeles.

A caution for the holidays: Don't be too eager to give up your seat. Full flights may mean you won't get to your destination in time.