Rental fraud is rising sharply, the BBC has learned during an investigation in which it confronted two online fraudsters for their crimes.
Scam artists offer cheap flats for rental, demanding instant deposits. But they do not actually own the homes - and would-be tenants' cash is lost.
Reports of rental fraud in England and Wales leapt from 2,216 in 2014 to 3,193 in 2015.
BBC researchers posed as tenants to expose tricks used by fake landlords.
One advert fraudsters attempted to place on the flat-sharing website EasyRoomMate offered a plush Kensington apartment for just £700 per month, far below the market rate.
Atta Nasim, of Milestone Estate Agents in north-west London, called the price "crazy", adding that you would not get a garage for that price in the area.
When contacted, a woman posing as the owner and calling herself 'Luise' tried to convince a BBC researcher to wire over £1,400 to a branch of The Coventry Building Society to secure the flat right away.
Land Registry documents show she is not the legal owner of a property there and when researchers visited the mansion block it was to find all the flats inhabited. The BBC also confirmed with the owners a 'Luise' was not associated with the property.
In an attempt to convince the BBC of the veracity of her offer, the fraudster emailed both a contract and a passport image in the name of a German lady.
The BBC has since established the fraudster has stolen the identity of a real German woman.
A second fraudster, calling himself Gary, offered a handsome red-brick period flat in Willesden on the same website for well below the market rate, urging the BBC's researcher to wire £1,500 to a Halifax account.
In reality, the property was home to Italian students. The managing agents knew nothing of 'Gary'.
'Gary' claimed to be based in London - but a BBC analysis of his IP address showed he was in fact communicating from a computer in Lagos, Nigeria.
Confronted with his lies by telephone, 'Gary' replied: "I don't know about that. You think this is a fraud? There is no fraud my friend."
When accused of taking part in a crime, 'Luise' put the phone down. The BBC's technical analysis showed she was in the UK.
The BBC has made the Coventry Building Society and the Halifax aware of the fraudulently-used accounts.
A Halifax spokesman said: "We are currently investigating the matter you have raised with us and will take the necessary action we deem appropriate pending the outcome of this investigation."
Student Nikola Poncet, a victim of the crime, lives in a small bedsit in Luton. He was ripped off by a fraudster with a bogus advert offering a flat in Queen's Park, west London, and lost £600.
Mr Poncet said: "I was willing to take the flat without a viewing based on the location, just on the price of it.
"[I felt] anger, disgust, I was really disappointed.
"I was thinking, 'Wow I've spent money I couldn't afford and what's happening to me right now? I'm in a nightmare and I can't wake up'.'"
The figures showing a rise in rental fraud were from Action Fraud, which collates national fraud statistics for City of London Police.
A spokeswoman for Action Fraud said it was working to stop those fraudulently advertising properties.
She continued: "We work with property adverting websites to ensure that they are able to recognise fraudulent advertisers."
EasyRoomMate, one of the largest flat-sharing websites in the UK, filters adverts before they go live.
It blocks 5% of the 1,000 adverts placed on its UK site each week because they are suspected to be fraudulent. But a further 1.5% that slip through the net are taken down after publication.
Albin Serviant, CEO of EasyRoomMate, which assisted the BBC in identifying the two fraudsters, said of the criminals: "They are very experienced, they are very sophisticated and they are also adapting very fast.
"They are very creative so we need to make sure the team are experienced enough to cope with these kinds of issues."
The adverts the BBC investigated were not allowed to go live by EasyRoomMate. Websites including Gumtree, Air BnB and Spare Room have also been targeted by rental fraudsters.
But for Mr Poncet, warnings come too late. He added: "I've got to start all over again."