An Inchcape Retail Mercedes-Benz dealership, part of the group that wants to be the world’s “most customer-centric business”, has been accused of quoting £4,376 for a service job that cost £36.25.

Mark Cornwall, a director of mail order company Car Parts Direct, says Inchcape tried to “cheat” him, an allegation rejected by Inchcape and Mercedes. They both say the dealership dealt with Cornwall correctly.

His six-year-old Mercedes C-Class was towed to Mercedes-Benz of Mansfield in Nottinghamshire after breaking down. Cornwall says the service manager gave him an estimate of £2,654.75 for parts and £1,700 for labour.

Instead, he asked SW Auto Services of Mansfield to investigate the breakdown, caused by water entering the fuse and module box. The protective lid was missing.

Steve Ward, a self-employed mobile mechanic who trades as SW Auto Services, said: “I used a specialist spray for cleaning and drying parts to resolve the problem. The car is still running, and what I did was a repair to resolve the problem, not a quick fix.”

Cornwall, whose company supplies SW Auto Services, says he has 25 years’ experience in supplying vehicle parts. He denies seeking publicity was the reason he issued a press release about his experience: “It was a personal matter.”

Inchcape says he signed a document requesting a valuation on his car – Cornwall denies “knowingly doing so”.

Ken Lee, head of corporate communications at Inchcape Group, referred AM’s enquiries to Mercedes-Benz UK.

Rob Holloway, M-B UK senior spokesman, said: “Mr Cornwall was given a quote based on a worst-case scenario, which the dealership believed was important given the age and value of the car. We and Inchcape believe the dealership acted properly.”

In a statement, Mercedes-Benz UK added: “The fusebox lid had been removed, allowing water into the electrical system, causing extensive damage. The retailer’s technical team assessed the damage and recommended the still-wet electrical system be replaced.”

The statement said that a Mercedes-Benz technical expert believed the now-dry car might work with some electrical cleaner, but “there was evidence of water damage and the system should be replaced to ensure the car was repaired to a satisfactory and guaranteed condition”.

Mercedes said the six-year-old car was out of warranty and had no documented service history. “The safety of our customers and other road users is very important and when sensitive electrical equipment is damaged to this extent it is recommended to be replaced,” it added.

“The company has at every opportunity worked hard to help the customer and the allegations and accusations do not give an accurate picture of the situation.”