It's incredibly frustrating for us all. Craigslist, Zillow, Trulia, and many others are all inundated with fraudulent posts. It seems we've found the evil side of technology. Many of my teams listings have been used in these scams and it's heart-wrenching to hear from the victims who call us as an afterthought because they drove by the home and saw our for sale sign. The problem is, there is no verification process when a listing is posted to public sites. Almost all real estate for sale listings in the actual MLS (member paid subscription with very strict rules and fines) are posted via a third party provider, but anyone can go directly to these sited or use postlets.com to post their listing directly to many of the most used home search sites.
Best of luck to you.