Motorists believe mechanics have overcharged them by a total of more than £800 million, a survey has found.
One in seven (14%) claims to have been ripped off when paying for repairs, with the average person cheated out of £155, according to the research.
Car maintenance app company Engie, which commissioned the study, said the figures suggest 5.4 million British drivers have been overcharged by a total of £833 million.
The poll of 1,300 motorists found that four out of 10 (42%) mistrust mechanics, while 12% believe they have been sold something their vehicles did not need.
Engie co-founder Gal Aharon said: "Mechanics may not actually be ripping customers off, but the research demonstrates the extent of UK drivers' lack of confidence in mechanic quotes.
"They simply don't understand what is being sold to them and if it's really necessary."
The amount that drivers believe they have been overcharged is highest in Edinburgh at £248, while the lowest is in Southampton at just £103.
Around one in 10 (11%) drivers admits to having a poor understanding about the health of their car, with nearly a quarter (23%) saying they do not understand any technical automotive terms.
Steve Gooding, director of motoring research charity the RAC Foundation, said: "Over the past decade, the average cost of maintaining a car has risen by about 40%. This is more than the rate of inflation and almost twice as much as the growth in wages.
"It's unsurprising that drivers want to believe they are getting a good, or at least fair deal, every time they visit the garage.
"Anything that causes car owners to cut back on servicing risks costing them more in the long run, and also means their vehicle might not be road worthy."