You don't say whether the listing you are referring to is for a property for sale or a property for rent. Rental scams are far more common. Some red flags for rentals include absentee owners, for example, if they say they were transferred out of the country for their job. If they ask you to wire money, especially out of the country, walk away, it's a scam. And, unfortunately, if they say they are missionaries or something of that nature, probably a scam. And, of course, if the price is too good to be true, it probably is a scam.
As far as sales of homes, the listings some people refer to are not really scams, but they are mis-understood. Realty Trac is a service that lists homes here and on other web sites that appear to be for sale but are not, necessarily. These are foreclosure and pre-foreclosure listings that are obtained from the county clerk's office when a bank files for foreclosure. These homes may or may not be available for purchase.
I either case the best way to protect yourselves from scams is to work with a licensed real estate agent.