This is why it is important to work with a reputable agent. If you just found bunch of listings on line there is no guarantee that they are real and have been advertizded by a real estate professional.
However, to minimise your risks when you are going for a showing appointment, you can always ask a person for their license or even for a copy of their license and call their firm to check if such a person in fact works there,
If apartment is shown by the owner (it has to be a condo or a coop, or a townhouse when talking about Manhattan) - you can look up ownership documents and ask for a copy of a deed on their name. All property records are public information and can be easily verified,
You also, have the right to request identification from the person renting out the unit if you believe they might be dishonest. Finally, you can insist on meeting the person in their office space and the next time you meet with them write down the license plate for the car they are driving.
Finally, I would always strongly suggest you work with a realtor who can help to verify the legitimacy of the rental. I forgot to mention that you should also check the foreclosure status of the property before you sign the lease. This will help you to avoid scams. You can check the foreclosure status of any property in the USA for FREE at http://www.nyhousingcenter.com
If you need realtor assistance I am available 24hrs at 914-299-0420.
A common scam is that someone has a key, lets you in, shows you around, and says they need $X in cash right now to "hold" the apartment until tomorrow, or even later today, when the lease will be ready. You show up tomorrow and, of course, the scammer doesn't. For many apartments there are enough keys floating around that former tenants can sell them to scammers if they don't want to do this con directly.
Another common ploy, one I have received many calls about, is the "rental" of an apartment that is actually only for sale, and I'm the listing agent so I know. Scammers take my for-sale ad info and turn it into a rental at a great rent. Then there is always a story about why they can't meet you, but they do need you to wire a good-faith deposit to rent the apartment. Sometimes these cons show a cell phone number in New Jersey, say, but the scammer is actually overseas somewhere.
These cons are very good actors, and they are creative. Usually it is a parent who searches for-sale listings and then calls me when they find the same apartment listed for rent and for sale (a rare situation anywhere in NYC, although it does happen). I remember one account when the con had convinced the student/parent that might not qualify to rent, but that the con would work with them despite their "marginal" finances! They had already turned over their financial disclosure info to the con, which put them at risk for identity theft too.
For small building rental situations, to make sure the person with the key can actually rent the apartment requires searching public records on line. I was a journalist for over 20 years, so I also ask a lot of questions during the site visit and make observations to see if the story adds up.
Remember that in New York State, only an owner or an employee of the owner (for example, the live-in custodian) can legally show an apartment to a prospective tenant without a real estate license. A current tenant can open the door and let you in. But any showing by a "friend" or "neighbor" of the owner is immediately suspect and you should leave these situations. Incidentially, you also don't want to be robbed.
To avoid rental scams, at a minimum you have these choices: 1. Work with a real estate agent; 2. Rent only from established rental buildings with rental offices; 3. Do a site visit and also investigate the purported landlord to ensure property ownership.
Licensed Real Estate Salesperson
New York, NY