Car rental customers in the U.K. are regularly being overcharged for repairs, according to an investigation by U.K. consumer rights group, Which?.

According to The Guardian, the investigation found that customers were frequently charged for damages they believe they didn’t caused. One customer was charged 1,000 British pounds ($1,388) for a windshield chip that could have been repaired for 35 pounds ($48), an increase of 185%.

Which? collected photographic evidence from agencies across Europe including Eruopcar, Green Motion, Avis, Budget, and Hertz.

In eight out of 12 cases, the consumer group deemed the car rental agency overcharged the customer; in four cases, it was determined the rental agency charged more than double the average quote given by Trusted Trader garages, a repair chain used by Which? to determine fair vehicle repair pricing.

A survey of 150 readers found 44% believed they had been charged excessively and 18% for damages they didn’t know about. Close to three out of five respondents did not receive a breakdown of the charges showing how the repair was calculated.

The Guardian reported that Avis, Budget, and Hertz told Which? that repairs are sometimes delayed until several damages can be repaired at once, and often, they are not carried out entirely. The rental groups said the bill a customer receives is an estimate based on a “damage matrix” of charges.