It is difficult to estimate the number of buyers who have been ripped off over the past few years, but Cardiff car dealer Graham Gamer believes there could be thousands, most of whom are unaware.

Those behind the scam purchase vehicles that have been declared a "repairable write-off" by insurance companies in other states. The vehicle is repaired to a roadworthy standard and re-registered for sale.

What prospective buyers don't know is that the car is worth half of what the seller is asking.

A NSW REVS check will show any financial or legal issues a vehicle may have in NSW, but it does not record whether a vehicle has been written off in another state.

Mr Gamer said a recent example involved a Hunter buyer of a Toyota Hilux 4WD. It was bought locally for $20,000 and was given the all-clear by a NSW REVS check.

But a V-check revealed the car had been written off in Queensland. The estimated value of the car dropped to $10,000, Mr Gamer said.

"It's as big as the drug trade," Mr Gamer said.

"The shonks are buying up cars in Queensland and Victoria, doing them up in their backyards. They've got a mate who'll give them a blue slip [in NSW] and then they sell them."

What frustrates Mr Gamer, a past president of the Motor Traders' Association, is that Queensland has the solution: a V-check, costing $14, shows if a car has been written off in any state or territory.

Many buyers and sellers aren't aware of V-check and rely on a NSW REVS check.

An RTA spokesman said the RTA and the Department of Fair Trading had been in discussions about the issue.

"The RTA will be introducing improved information to the NSW public later this year . . . in relation to vehicles with NSW registration," he said.