The Automobile Association says complaints show used-car dealers are illegally putting worn parts back into vehicles before selling them on.
"Certainly we see that it is going on," said Stella Stocks, AA's general manager of Motoring Services.
"The problem with this issue is until it surfaces the way that it has, no one knows about it."
Yesterday the Herald reported that the Auckland Motor Vehicle Disputes Tribunal ruled on three cases in the past year where a dealer had illegally swapped parts.
When used-cars are brought into the country they are subject to a safety test, performed by one of three organisations which include the AA.
Very often worn parts will have to be replaced before the car is re-checked by the compliance agent and allowed to be sold.
In its annual report the tribunal said it believed dealers were putting the old parts back into vehicles after getting approval at the recheck.
Ms Stocks said the AA was often approached by motorists who bought a car which had been given the all-clear from the AA, but had subsequently had problems.
"They come back to us and say, 'You did the entry certification on this, and look at the tyres on this car - they're not suitable'.
"We know from the documentation that we keep on compliance that those particular tyres, or whatever it may be, were not on the vehicle at that time."
The NZ Transport Agency is currently attempting to determine the extent of the practice.
The Auckland tribunal said cases it dealt with could be "the tip of the iceberg", or confined to a few dishonest traders.
The traders accused by the tribunal and the Imported Motor Vehicle Association say swapping parts makes little financial sense.
Yesterday that was supported by automotive engineer Brian Felton, who represented licensed dealers on the Auckland tribunal for nine years.
Mr Felton said while some dealers took shortcuts, he could not believe the practice took place, given the relative cheapness of parts like brakepads.
But Ms Stocks said the problem could well be widespread, particularly because many victims would not work out what had happened.
"The reality is to a lot of people a car is a mode of transport ... the technical details they've got no idea on."
* Used-cars checked for safety upon importation by compliance agent such as the AA.
* Very often dealers told to replace worn or damaged parts.
* Once this is done vehicle is re-checked and given approval for sale.
* Some dealers accused of then putting old parts back into car before selling on.