Scenario 1: You have a nice little investment property that you rent out. It's low maintenance and the rent you pull in is enough to pay the mortgage, so there's not much risk. But one month, the check doesn't come in the mail as it usually does.

You go to the property to give the tenant a stern talking to, when you find another tenant altogether! Not only have you never seen this woman before, she tells you she gave the rent to someone else in cash! Now you're faced with either kicking her out or paying the mortgage without your rental income for several months.

Scenario 2: You find a rental property online. It's a good deal, and the renter says he'll give you an even better one if you pay cash, in advance, for the first six months. He shows you around and you love the place so you snap it up. A few weeks after moving in, a man shows up claiming to be the landlord. He says you owe him rent, or he will kick you to the curb. You insist that you've already paid rent, but to a different man. He tells you he'll have to get the police involved.

Explanation: Your last tenant decided to move out, but didn't tell you. Instead, he spent the last month of his stay posing as the owner and trying to rent out your place. He handed over the keys and collected the rent in advance for the next 6 months. You will likely never see this man again.

How to avoid: as the owner of the property, always ask for pieces of ID from the renter. It just makes it easier if you need to track him down. As the renter, be very wary of deals that are better up cash. If you need to, ask to see proof he is the property's owner