These photos capture a suspected gang accused of scamming people selling second hand cars by damaging the vehicles during viewings and then offering knocked-down prices for them.

Police have launched an investigation into the group, who have been operating in Norfolk.

They gang identify vehicles through online adverts and then arrange viewings, during which - unseen by the sellers - they cause damage or create apparent flaws.

They then point out the problems and try to buy the car for a reduced price. If successful, the gang are then able to easily repair the vehicle and restore its original value.

Online car seller AutoTrader has warned customers about the group and confirmed it has received several reports of this happening.

In one incident last Thursday at a house in Foulden, south west Norfolk, the group poured oil over a BMW's engine, including in the radiator coolant reservoir and then claimed it had an oil leak and asked for a reduction.

The man, who was selling the car, told this newspaper that three men had turned up. Two had distracted him by looking at the service history in the boot of the car, while the third man played under the bonnet.

He said when they pointed out the supposed oil leak they asked him for £400 off and he refused. They then reduced it to £200 and he again said no and they drove off.

He only realised what they had done when he watched his CCTV footage later. He called the police who fingerprinted his vehicle. He then had to flush the engine and the car is now working again.

Another report suggested that the gang interfered with the wiring of an engine, causing a warning light to go on - a problem they would have been able to easily rectify once they had purchased the vehicle.

Sellers contacted by phone numbers associated with the gang have been sent a message by AutoTrader telling them to watch out.

One man in Dereham, who did not want to be named, was contacted in January on several phone numbers by people from the group.

He arranged for a viewing of his BMW 5 Series last week. But before the interested buyers arrived, he received a message from AutoTrader warning him of the possible scam.

He then spoke to someone in AutoTrader's security team, who said they had complaints from other sellers about the group damaging the engine during viewings.

The man decided to go ahead with the viewing so he could film the gang when they visited on February 3.

“They started touching the engine and sides," he said. "But the moment they saw me filming they got irate and told me to turn the camera off. They then scarpered."

The group drove away in a silver Audi. The pictures have been shared with the police, but we are concealing their identities for legal reasons. Norfolk police have said officers are investigating the scam.

An AutoTrader spokesman said: "We actively assist law enforcement to prevent and detect criminal activity or apprehend offenders.

"We take preventative and detective action as soon as we are made aware of issues, and use a number of different technologies to monitor and prevent fraudulent activity on our site.

"We alert customers if we have identified any activity that we believe isn’t legitimate."

AutoTrader advises sellers to never leave a potential buyer alone with the vehicle or give them the keys.

They added: "Wherever possible, have a friend or family member with you. Always arrange to meet a buyer at your home, never meet halfway or at their premises."

How to avoid being scammed

AutoTrader said it provided tips on its site to keep people safe. They include, never sending money for vehicles you had not inspected and keeping keys safe during viewings.

When it receives complaints it also alerts other sellers if they are contacted by that same buyer's phone number.

In 2006 it established the Vehicle Safe Trading Advisory Group (VSTAG) ) with the aim of bringing together law enforcement, trading standards and other key classified marketplaces to share advice. The group introduced a introduced a minimum set of standards across the industry.

-Anyone with information should contact Norfolk Police at: investigate@norfolk.police.uk quoting crime reference 36/9597/22.

-Alternatively contact Crimestoppers anonymously on 0800 555 111.