Complaints about second-hand cars rose by 18% in the year’s first six months compared with the similar period of 2009, the Office of Fair Trading says.
It said the advice service, Consumer Direct, took just over 38,000 complaints about used vehicles bought from dealers.
Its study found that many car buyers discovered faults in their vehicles only once they had driven them away.
The OFT is warning buyers to check their rights before settling a deal.
The motoring organisation, the AA, called the findings “alarming”.
Some 3.6 million used cars are bought each year in the UK, costing a total of £24bn.
The study found that many motorists ended up fixing problems with their new purchase themselves, at an estimated average cost of £425, when in fact they were the dealer’s obligation to correct.
Consumer Direct receives more calls about motor vehicles than anything else, above mobile phones and TVs.
Its operations manager, Michele Shambrook, said: “Dealers have a responsibility to sell cars that are of satisfactory quality.
“This will vary depending on issues including the vehicle’s age and mileage, but as the vast majority of all second-hand car faults come to light in the first three months, they will often be the dealer’s responsibility to fix.”
AA president Edmund King said: “With two-thirds of used-car buyers spending less than a fortnight to choose a car, while many will spend months planning a holiday, rip-off merchants are handed easy pickings on a plate.”
He said although car buying was typically the second-biggest purchase most people made in their lives, it happened relatively infrequently, so buyers forgot the pitfalls and often let their heart rule their head.
The OFT and Consumer Direct have compiled a checklist for potential buyers, including questions about the car’s mechanical history and mileage checks, the number of former owners, documentation about the full service history and any modifications.
They also urged buyers to get the answers in writing rather than relying on verbal claims or promises by the seller.
This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.