A new episode of BBC Watchdog warns car buyers about the dangers of buying a vehicle from a dishonest seller.
While a third of vehicles examined byHPI are revealed to have a concealed history, a surprising number of second-hand car buyers do not have their vehicle checked before they hand over their cash.
HPI is urging car buyers to check that the sale is legal before any money is exchanged.
The Watchdog investigators probed a firm that was offering vehicles with obvious faults and persuading unknowing used car buyers into wasting their money.
The report shows that unscrupulous dealerships are also selling cars at a higher price than their retail value. HPI advises buyers to conduct prior research into pricing and to have the vehicle independently checked before a sale.
"This Watchdog episode reminds us how easy it is to be duped by smart sales patter and a friendly approach," said Nicola Johnson at HPI.
"Too many used car buyers take the seller's word at face value. This leaves them at risk of being told a pack of lies and spending good money on a car that turns out to be a nightmare on wheels."
She added that some sellers are also telling buyers that once the car has been sold, any problems are the buyer's responsibility and that any legal rights had been relinquished. This is not true, and underlines the importance of buyers being aware of their rights, she said.
Copyright Press Association 2013