I run online classifieds in another venue. One of my sellers was scammed. Since then I have offered this info:

If you have been a VICTIM of the Nigeria Counterfeit Check Scam (or any scam like this), contact the US Secret Service, the lead agency fighting this fraud. Call 202-406-5572, or write to: US Secret Service, Financial Crimes Division, 950 H Street, Washington, DC 20001. Send complaints to the Secret Service at http://www.secretservice.gov/contact_fcd.shtml.

It amazes me how these people infiltrate the market.

DJ