Car owners selling their vehicles privately are being warned of a dirty trick that could see their car plummet in value.
Fraudsters are deliberately sabotaging vehicles they go to view in an effort to force the seller to drop the price.
Motorist Michael Browne is warning other drivers to be on the lookout after being targeted recently.
Building company director Michael advertised his Volkswagen Toureg online and a prospective buyer turned up to view the car with a friend and a boy aged around 11.
They looked around the car then took it for a test drive. During the drive smoke started billowing from the car, after which the buyer asked to see the engine again and claimed the smoke was a sign the car needed a new engine. He then offered Michael just a third of the Â£3,600 asking price.
Michael said: â€œWe parked up and he asked to look at the engine again and then he dipped his finger in the coolant and showed me the dirty oil and I tried it too.
“But I’d topped up the coolant about two weeks ago, so I knew it had been clean.
“That’s when I started thinking something was up.”
Michael believes that while one of the con artists distracted him one of the others used a squeezy bottle to contaminate the coolant with dirty oil.
“While one was looking at the engine, the other one wanted to look at the spare tyre so they got me around to the boot,â€ he explained.
“That must have been when the young lad who was around the front put dirty oil in the coolant.
“I think they used a squeezy bottle.
“While I was looking at the engine, he must have put some in the exhaust pipe.”
The buyers tried to negotiate but Michael spotted a patch of oil under the car and asked them to leave after realising they were trying to trick him.
“I still wasn’t sure it was a scam but then I looked it up and found it’s very common,â€ said Michael. â€œIt’s quite an old scam.”
Michael took the car to a garage where the system was flushed through and after posting about his experience on social media heard from several other victims.