I recently had problems with a transaction and I contacted these folks. They contacted the law enforcement agency in the guy's hometown. While I can't say 100% that getting these people involved was the reason why the person I was dealing with had a sudden change of heart, they did take action fairly quickly. I had thought I wouldn't hear from anyone anytime soon but they must have contacted the law in my behalf within a week. I received a letter from the local law enforcement agency the same week after the guy finally sent my money saying they had contacted him.
http://www.ifccfbi.gov/strategy/howtofile.asp
http://www.ifccfbi.gov/strategy/howtofile.asp
