One of the most common complaints I get from car rental customers is that they’re being charged for damages that they weren’t responsible for. They wonder if the companies are double-dipping — charging multiple customers for the same repair — as at least one franchisee has admitted to doing. But proving that kind of behavior is difficult.

Not to Cynthia Plume, a reader who I advised on her recent damage-related grievance with Thrify.

When she picked up her rental car at the airport late at night in Sarasota, Fla., there was no apparent damage to the vehicle. “We drove it several miles to our home,” she says. “The next morning, as we walked into the garage to leave, we noticed that the front end of the car had been damaged.”

She called Thrifty to report the condition of the car, and was told not to worry about it. The damage was pre-existing, and a representative assured her that anyone reviewing the file would see the report and she wouldn’t be charged.

That didn’t happen. After she returned the car, she received a $700 bill for the dent.

She called me to find out what to do next. I urged her to send a cordial but firm email to Thrifty, asking to substantiate the charge with repair records.

Thrifty backed down almost immediately, sending her a letter that her case had been “closed.”

Plume phoned the company to find out what had happened. “A customer service representative looked up our reservation, and she could not explain it because the file did, in fact, show a damage report prior to our rental,” she says. “It also showed our phone call and the customer service rep’s notations related to the previous accident report.”

The Thrifty agent went on to say she had “no idea” why Plume received a claim.

“Strange, huh?” she adds. “Double dipping? Maybe. Bogus claim? For sure.”

If you suspect you’ve been the victim of a double-dipping scam, send me a or leave your comments below.