While most landlords enjoy a comfortable relationship with all their tenants, letting property has always had the potential for big problems: the two biggest concerns being will the rent be paid in full and on time and will my tenants take care of their home?

Most landlords, and especially those using a reputable agent, will make exhaustive checks on an applicant's finances and previous renting record before handing over the keys. However, according to Landlord Action, a company that helps landlords remove rogue tenants and recover the rent, there is a growing number of bogus tenants stalking the streets of London.

The latest con is bad news for genuine tenants too. A seemingly respectable woman in her early forties has to date rented three large houses in central south-west London and passed seemingly rigorous checks on her background. However, within days of collecting the keys she sub-let the houses to perfectly innocent tenants who paid her a reasonable rent that she pocketed and of course did not forward to the real landlord.

She now owes more than £30,000 and has already appeared once in court. Not only are the owners of three houses out of pocket but the people living in them, who paid rent as well as a deposit of six weeks' rent, now face eviction and the loss of that deposit.

How could this situation be avoided? The woman used aliases and had rogue referees backing up her story, and one of the owners who met her described her as charming, but more and more estate agents are sharing information on bad tenants and the best agents often have a gut feeling about conmen.

If you have any doubts, walk away or check further into their background: one serial bad tenant claimed to work for a hedge fund and earn a six-figure salary but when the reference agency looked up the address of his so-called employer, it turned out to be a one-bedroom flat in a high-rise council block.

More and more agents are turning to social networking sites, such as Facebook, to check out their tenants, not only to find out a little about their background but also for hints about their behaviour. It might be an idea not to post pictures of a wild party at your previous address, nor to brag about the damage that was done.

Tenants worried about the bona fides of their landlord can check out who really owns it through the Land Registry, although, again, using a good agent should guarantee some security.