The victim had been in contact with his attackers on Gumtree
Open heart surgery was needed to save a man stabbed in east London after going to buy a car from someone he contacted through the website Gumtree.
The victim, 42, went to Barking to buy a VW Golf advertised on the site.
But he was ambushed, then beaten, kicked and stabbed in the heart, lungs and abdomen, before the £5,000 he was to pay with was stolen.
The car's true owner was unaware it had been offered for sale. Two men have been arrested by police and given bail.
The incident happened on 30 July, but details have just been released by police who are desperate to find more witnesses.
Describing what happened, Det Ch Insp Ellie O'Connor of Barking CID said: "It was broad daylight and a busy area so the gentleman thought he would be safe.
These men were not messing about and it is but for the skill of the emergency services that he survived
Det Ch Insp O'Connor
"He could not see the car, so he put in a call to the seller.
"Then he was ambushed from behind and knocked to the floor where he was beaten, kicked and stabbed four times."
Det Ch Insp O'Connor continued: "Thanks to the intervention of a member of the public they ran off.
"The passer-by then gave first aid until the air ambulance arrived."
The victim, from north London, suffered a injury to his heart's pericardial sac and a collapsed lung, among other injuries.
'Safety taken seriously'
Although expected to recover, he is still too traumatised to discuss the incident, which police described as a "life-changing experience".
Det Ch Insp O'Connor added: "These men were not messing about and it is but for the skill of the emergency services that he survived.
"He will take two months to recover."
A Gumtree spokeswoman said: "We take safety very seriously and regret that one of our users has been a victim of crime.
"We work with law enforcement officers to keep the site safe and are helping police with this investigation."
She added: "We strongly recommend that users meet in daylight, in a public place and take a friend." http://news.bbc.co.uk/1/hi/england/london/8222087.stm