Rental scams are common here and on any site that allows the general public to post. Please be very cautious with deals that seem too good to be true. NEVER send money expecting keys back by mail.
You can search the address in any search engine to see how the homes are advertised elsewhere. If one listing is much cheaper than other places, it's likely a scam.
Read the scam warning Trulia posts. I've attached a link to it below.
When you find a questionable listing please go to the More button on the listing and then hit the FLAG button on the listing page to warn Trulia and others or email it to Rentalfraud@Trulia.com.