Allison Preiss became a hero to airline passengers this spring when she scored a $10,000 travel voucher for losing her seat on an oversold flight.

Negotiating skill mixed with a bit of luck helped Preiss land the elusive payoff.

With the peak summer travel season right around the corner, other passengers can learn from Preiss’s example if they wind up on an overcrowded flight.

There are two situations that passengers might find themselves in, and their rights — and bargaining power — vary greatly between them.

In the first, an airline forces a passenger off a flight for lack of space — called bumping. Under federal rules, the passenger is entitled to cash compensation, not just a voucher, and a seat on a later flight. Bumped passengers whose travel is delayed for at least an hour are entitled to up to $1,350 in compensation, with the amount based on the length of the delay and the one-way price of the ticket.

“The vast majority of Americans take one airline trip a year, and since vouchers are usually valid for just one year, most people should ask for cash,” said George Hobica, a travel expert who founded the airfarewatchdog.com website. But, he added, frequent fliers might want to negotiate to see how high the airline will go with a voucher.

That’s what Preiss did back in March. Thanks to a broken seat, United bumped her from a flight from Dulles Airport outside Washington to Austin, Texas. But Preiss had leverage because United couldn’t find anyone willing to give up their seat. She calculated that she was entitled to about $650 in cash based on the price of her ticket, and she turned down a $2,000 voucher. Then a second United employee said she could offer a voucher up to $10,000 plus a seat on a later flight, and Preiss took it.

The second situation occurs when the airline hasn’t yet kicked anyone off an overbooked flight but instead looks for people to take a later flight in exchange for compensation — usually a voucher; the airline is not legally required to pay cash to volunteers.

When airlines know a flight is overbooked, they will make lowball offers to customers at ticket counters, kiosks and gate areas. They will raise the amount of the vouchers until they find a taker, pitting passengers against each other in a kind of reverse auction.

“My advice would be to start high,” said Brian Kelly, CEO of travel website The Points Guy. “If you’re going to be displaced for several hours, don’t take the quick and easy $200 (voucher).”

Kelly said a $400 voucher for getting off a domestic flight or $800 for an international one would be “a solid starting point.”

Travel experts suspect that airlines prefer vouchers partly because a high percentage of them never get used. The airlines do not disclose redemption rates.

Airlines have gotten very good at buying off passengers on overbooked flights. Last year, about 23,000 passengers were forcibly bumped — the lowest rate since the federal government started keeping track in 1995 — while nearly 342,000 people took an airline’s offer and gave up their seat.

You might wonder how airlines ever come up short on seats.

Airlines can legally oversell flights — although some, like JetBlue, say they don’t — on the assumption that some people won’t show up. Overbooking can also occur when bad weather or a mechanical breakdown causes flights to be canceled, forcing the airline to scramble to accommodate stranded passengers.

Sometimes airlines switch a flight to a smaller plane with fewer seats. Occasionally, they need to make room for an air marshal or employees. And airlines may cancel flights or limit seating on smaller planes in hot weather because the thinner air makes it harder to generate enough lift for takeoff.

If you take a voucher for getting off a flight, there are some rules you should know. For instance, most airlines won’t replace lost vouchers, and they can’t be sold, although Delta allows them to be transferred to someone flying on the same reservation as the person who got the voucher.

On Southwest, vouchers can only be applied to airfare while American also lets them cover taxes and fees and Delta vouchers can be applied to government taxes. But you can’t use vouchers to purchase extra legroom or an in-flight meal.

If your airline looks for volunteers to get off an overcrowded flight, experts offer this advice before accepting a voucher:

— Insist on a confirmed seat, not standby, on the next available flight in addition to the voucher for future travel.

— If you will be stuck for an extended time, ask for meal or hotel vouchers too.

— Ask when the travel voucher expires — typically they are good for one year — and whether it can be combined with other discounts.

— Find out if the voucher can be used on other airlines; American and Delta vouchers can be used on some partner airlines, United and Southwest certificates cannot.

Kelly, the travel-points expert, advises that no matter what, “don’t get stressed.”

“Look at it as an opportunity for a nice little payday.”

(AP)