You can go to an internet fraud site and file a report. I did with a guy on ebay that was selling camera lenses. They ran somekind of investigation and I got my lenses from him. I dont know exactally what they did to him other than sending him a threatening letter but maybe it will help you. It was awhile ago and I dont have the site listed anymore but this one may help you out.
http://www.internetfraud.usdoj.gov/
Here is where the forms are I think.
http://www.ifccfbi.gov/cf1.asp