To understand why, it helps to ask how damage disputes happen. Industry experts say it's often an innocent mistake by one or both parties.
"Hundreds of vehicles may be returned within a couple of hours," said Neil Abrams, president of Abrams Consulting Group in New York, a consulting and market research firm for auto rental and allied industries. "It could happen that a vehicle is not examined carefully on check-in, and damage is discovered later. Or a customer may not have noticed the damage." Days later, the renter may get a repair bill in the mail.
Fraud can happen too.
Two years ago, the Arizona attorney general's office obtained a $139,000 consent judgment against a car-rental outlet at the Phoenix airport that it said falsified repair notices and improperly billed at least 80 customers for windshield damage.
"In some cases, two people were charged for the same chip damage" and billed about $200 each, said Nancy Anger, the assistant attorney general who handled the case.
Abrams, who called the Phoenix case "highly extraordinary," said rental companies are not in the business of making money on damage — or alienating customers. But they may be less inclined to overlook dents, scratches and scrapes these days.
"There is greater diligence in pursuing damage claims," he said.
One reason: With rental stations keeping about 25% fewer vehicles on hand than in the boom years of 2006-07, taking a car out of service for repairs becomes a bigger issue, he said.
Whether a damage dispute stems from carelessness or something more sinister, documentation can win the day.
If you leave the parking lot without it, "it's just your word against the rental company's word," Anger said.
Here's how to protect yourself, based on suggestions from Abrams, Anger, Bay Area travel attorney Al Anolik and Philip Reed, senior consumer advice editor for Edmunds.com, an automotive information website.
Deal with a human: When picking up and returning your car, ask a staff member from the rental office to examine it, circle any dings and dents on a form and give you a copy. Avoid using a program that allows you to choose your own car from the lot or bypass the counter when returning it, which makes it tougher to dispute damage on the spot. "It's not worth it," Anolik said.
Take photos: Use your smartphone or camera to take snaps of your rental car, inside and out, before and after renting it. Include the license plate and the immediate area. Make sure the photos are time-stamped; many digital cameras and smartphones can be programmed to do this.
Decline unkempt vehicles: A car that clearly hasn't been cleaned since the last customer may not have been inspected for damage, leaving you open to blame when you return it. And dirt can conceal surface blemishes.
Check your insurance: You're probably covered for damage to a rental under your policy for your personal vehicle. Some credit cards also cover rentals. But if you aren't covered or your policy carries a hefty deductible, consider buying the collision damage waiver from the rental company. Although it can be costly, it may get you off the hook.
Complain effectively: Try first to resolve the issue with the rental car company. Ask for a manager.
"If there is a real dispute and the rental customer has a valid argument, mostly they'll work with the customer," Abrams said.
If that doesn't work, enlist the help of your credit-card issuer. Under the Fair Credit Billing Act, you are entitled to dispute charges. As a last resort, try complaining to the district attorney or the state attorney general.
Expect them to ask for proof. Arranging to rent a car can take long enough without taking time to document the car's condition. But in this case, time really may be money.