06/19/2012 12:59 pm ET

Car Rental Fees Continue To Shock Drivers

Have you ever felt duped by a car rental service? You're not alone.

California resident Don Nelson is the latest victim of errant fees and backless claims, according to a report by CBS San Francisco. Nelson drove a rented vehicle without incident until the final day of his rental contract, when the "check engine" light lit up on the dashboard. The vehicle was acting fine, and when Nelson returned it to Enterprise that day, he was told by the agent, "don't worry about it." A week later, he was served a bill for $145 for supposedly damaging the vehicle by revving the engine, according to the company's claim.

The local television station's consumer watch advocates went after Enterprise and the charge was eventually dismissed as a "mistake," but Nelson's experience isn't the first and won't be the last. Atlanta resident Carrie Finegan disputed an astronomical charge of $464 from National for a minor dent to her rental vehicle -- damage she insists did not happen while she was operating the car. After being threatened with having the bill reported to a collection agency, Finegan sought the help of author and consumer advocate Christopher Elliot, who managed to get the claim dropped.

While Finegan maintained her innocence, she had broken a cardinal rule of car rentals: Take photos. Jason Alderman, senior director at Visa, advises: "Before you drive off the lot, thoroughly inspect the car, inside and out, for any pre-existing damage and note it on your contract; otherwise you could receive a hefty bill for someone else's minor scratches and dents. Likewise, when you return the car, consider taking time-stamped photos or video to prove it was in good shape."

While some renters are hit with surprise charges after the fact, others are facing higher fees before they even leave the lot, thanks to what many rental agencies call "dynamic pricing."

In a report on Frommer's, rental client Hal Gordon complained of some odd pricing and booking policies by several companies, including Hertz and Avis. Gordon was doing some research for a friend from Israel, but, "the website said there were no vehicles available for the dates chosen," he told Frommer's. "I checked for other countries in the Middle East -- same result. However, for UK or Venezuela -- no problem. Vehicles were available," he said.

Gordon's inquiry uncovered a common pricing system that can alter consumer search results based on, "level of demand, cost of service, currency exchange rates, and the competitive environment," according to an Avis spokeswoman. Alderman suggests it's best to do your research ahead of time and use comparison sites like Hotwire or Priceline to see competing offers.

Have you been subjected to ridiculous car rental fees? Tell us about it in the comments.