Verify by making sure you're speaking with the legitimate landlord!
If you've seen a rental on trulia, or any other site, and the price seems almost too good to be true..more than likely it isn't true, and it's a SCAM!!!
If the supposed landlord says he or she can't show you the house in person (or simply that you can't see it in person) RUN in the opposite direction.....it's a scam! Many scammers have creative stories as to why they cannot show you the home (many say they are "out of state" or even go so far as to claim they are missionsaries!!)
Finally, if anyone ever asks you to WIRE MONEY for the keys....it's definitely a scam - do NOT do that!!
To really verify a rental - speak to a local agent!!!!