Used cars continue to top the number of complaints to the OFT, new figures released today reveal.
More than 56,000 people have complained to the OFT-managed Consumer Direct in the year to date.
The new statistics have been published by the OFT as it launches a Know Your Consumer Rights campaign to warn people about problems they may encounter when buying a used car.
As part of the campaign, the OFT has produced a short online film to inform people about their basic rights when buying a used car, and what to do if they encounter problems after purchase.
It is also working with local trading standards and the motor industry to make information on consumer rights more readily available.
Today's figures show more than 70% of the complaints were about faults with the cars.
More than 13% were about misleading claims or omissions by the seller, and 7% were about substandard services.
An OFT study published last year found that consumers are left out of pocket by an average of £425 each, or £85 million per year in total, because they have to fix unresolved faults that are the dealers' obligation to correct.
Michele Shambrook from Consumer Direct said: "We continue to receive a high number of complaints which are often due to some traders refusing to deal with legitimate complaints or provide appropriate compensation.
"We want to help people understand their rights when buying a used car from a dealer and we are working with the industry and local authority trading standards to get this message across.
"Dealers who fail to treat customers fairly or sell cars that are defective could face enforcement action."
Used car supermarket Carcraft recently was censured by the OFT over its sales practices.