The OFT has taken action against used car buying firm Webuyanycar.com after finding a staggering 96% of customers received less than the website's valuation tool suggested.
In some cases, the discrepancies amounted to hundreds of pounds.
The site is famous for its annoying TV and radio adverts which includes the jingle "we buy any car dot com".
The watchdog's investigation found consumers were given the impression they would be paid the online valuation if the company's onsite inspection matched the condition entered by the seller online.
But once at the appointment, some found other factors reduced the final price, including "market conditions".
The OFT also found vehicle inspectors were set targets, sometimes to reduce the valuation offered by up to 25%.
The company and its directors have signed undertakings to:
- Make clear the website valuation is not the price the company is offering and that a range of other factors might be considered;
- Not set targets for inspectors that may encourage them to reduce the valuation offered;
- Not deduct from the price any from the DVLA for the remaining road tax;
- Make it clear the next working day payment service (with a £24.75 fee) is optional.
Cavendish Elithorn, from the OFT, says: "It's important the headline figure isn't chipped away at by the buyer, because it makes it very difficult for consumers to shop around and find the best deal.
"This action makes clear online businesses must provide clear information on pricing and about how their service operates."
The OFT says the company and its directors believe their business practices complied with the law, though they have nevertheless agreed to make the necessary changes.
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