What was said above is good. Paypal is huge, always make sure the opposite party has a confirmed address and a verified account if you're accepting money from him.
Keep a paper trail - especially with the IFCC newly formed and active. Theft of virtual property can now bring charges and hold up in civil suits because of new legislation under Internet, Mail and Money Fraud. Most retarded scammers think they're untouchable, and that's not the case anymore.
If you get scammed, file a complaint and a report with the IFCC - you can Google their website under .gov domains. They usually contact you quickly, and can put you in touch with state agencies including district attornies.