In the first three quarters of 2016, carriers collected $3.1 billion in luggage fees, an increase of roughly $300 million from the previous year. (iStock)

Airport luggage scales lie.

It’s not an uncommon allegation. And sometimes, it’s actually true. Ticket counter weights in Phoenix, Raleigh, N.C., and Seattle have been found to be inaccurate — errors that sometimes enrich the airline.

Baggage fees are big business. In the first three quarters of 2016, carriers collected $3.1 billion in luggage fees, an increase of roughly $300 million from the previous year. Luggage scales are generally regulated at the state level and are subject to inspections quarterly or yearly, depending on their location.

The question isn’t whether airport scales are a little off , but what to do when you’re at the airport and a ticket agent announces that your bag is too heavy.

Your airline immediately sees dollar signs. For example, American Airlines charges just $25 for a checked bag on a domestic flight, but the fee quadruples if your bag weighs more than 50 pounds and doubles again to $200 if it’s over 70 pounds. Do the airline’s costs actually multiply by that much when your bag weighs an extra pound? That’s debatable.

The Weigh It is a stand-alone digital luggage scale. It attaches to your handle. (InventHelp)

Passengers, on the other hand, see red. They reflexively claim that the airline has its thumb on the scale . But that’s just the start of a peculiar airport game that’s winnable if you know how to play it.

“Delta and American ask you to remove enough to get it under the allotted amount,” says Rich Ruddie, who runs an online consulting firm in Fort Lauderdale, Fla. “And, of course, Southwest lets your bags fly free.”

Other airlines, though, take a hard line on overweight bags. On some discount carriers, ticket agents have given Ruddie an ultimatum when his bag tipped the scale at 51 pounds: Either pay their $55 overweight luggage fee or abandon the bag. “They milk you for every penny,” he says.

There’s a way to avoid confrontations, of course. Weigh your bag before you leave. You can either buy a stand-alone digital luggage scale such as the Weigh It (inventhelpstore.com; $19.95), which attaches to your handle and can be used for a variety of objects, not just luggage. You also can buy luggage with an integrated scale, such as Raden’s A22 (raden.com, $295) which will tell you your bag is overweight before your airline does.

Or you can come prepared to offload.

“I always have an empty, lightweight tote in a side pocket,” says Robert Kraus, who works for a political organization in Alexandria, Va. “Just in case.” He also offers some more un­or­tho­dox advice: “I always leave a little part of the bag, usually the wheel end facing me, on the edge of the scale,” he says. In the same vein, some travelers say that they are cut more slack when they check in curbside. The agents there, who often work for tips, are more likely to look the other way if you have a heavy bag.

Raden’s A22 suitcase includes tracking, a built-in digital scale and charger. (Courtesy of Raden)

Elisabeth Herbert, a counter agent for Alaska Airlines in Spokane, Wash., says arguing with an employee is often an act of futility. “I’ve had people argue with me saying our scales must be off,” she says. “I’ve noticed most of the time the bags are only overweight by two to three pounds.” She suggests that travelers leave themselves some wiggle room to allow for small discrepancies.

One of the most egregious luggage-fee cases that has crossed my desk was Janet Mosher’s. When she flew from Salzburg, Austria, to Frankfurt, Germany, on Austrian Airlines, a ticket agent tagged her checked bag and sent it along the conveyor belt. But her carry-on bag was deemed overweight.

“I could easily have met Austrian’s weight requirements by placing items from my carry-on in my checked bag, which was well below the airline’s weight limit,” recalls Mosher, a retired teacher from Alexandria, Va.

The agent offered her three choices: remove and discard items from her bag to reduce the weight, pay a 75 euro overweight luggage charge or transfer items from her overweight carry-on to another passenger’s bag, which was still on the belt and about to be checked.

“These ‘gotcha’ fees are capitalism at its worst,” she said.

I agree. It’s one thing for an airline to simply cover the cost of transporting your excess poundage, but the fee structure makes charging for overweight baggage look like the money grab that it is. Shouldn’t airlines be making money the old-fashioned way, by selling tickets? I contacted Austrian Airlines on her behalf and it refunded the 75 euros as a goodwill gesture.

And if all else fails?

“I turn up the charm and appeal to the agent’s spirit of generosity,” says Nick Bratton, who works for a nonprofit organization in Anchorage. It’s a strategy that’s particularly effective when you’re a pound or less overweight and you can find a compelling reason for the agent to look the other way — it’s a return flight or you’ve packed a gift for an elderly relative.

“This approach has been successful for me more often than not,” Bratton says. “But I don’t recommend it as much as planning ahead.”

Elliott is a consumer advocate, journalist and co-founder of the advocacy group Travelers United. Email him at chris@elliott.org.