Trulia is certainly better than a site like Craigslist where almost one out of tow rental ads are scams. That said, not site is completely safe from con artists and scammers. The best advice I can offer you is that if the owner of the property can't or won't meet you personally at the property to show it to you and give you a lease to review, move on you're being conned. Never send money to someone you don't know who promises to send you keys etc.
There are also professional property managers who post here on Trulia, but as above they should meet you at the property, show it to you, answer you questions, be able to give you a lease to review etc.