I was totally caught by this scam two years ago. I posted my rental on Craigslist and someone "copied" the listing and re-posted it for $300 less than I was advertising it for. Then when people called, someone answered and told them about it. Then they told them to mail money orders to their address. Thankfully I noticed and reported it, but I think at least 10 people called me directly thinking that was the amount I was renting it for.
I told one of the agents in my office the other day, if scam artists worked as hard at a legal profession...they would be millionaires. Make sure when you see a listing advertised for rent: does it have a company's name at the bottom, or a landlord? do they give a detailed description of the property? and finally, does the price seem too good to be true? NO landlord or property manager will ever ask you to send Western Union. They will have an office you can meet them in, or if it is a private owner, they will meet you at the property.