Deal locally. Follow the same common-sense precautions you would if listing or answering a traditional classified ad. Make deals with local people whenever possible so that you’ll be able to meet face to face.
Insist on cash. “Fake checks and money orders are common.” If you accept one as a payment, your bank will “hold you—not the buyer—responsible.”
Do some research. When you can’t deal locally, check up on the other party: Get a street address and look it up on a White Pages service such as whitepages.com. If there’s a listing, “that’s a pretty good start” toward establishing your counterpart’s baseline reliability. Google the person, too.
Pay cautiously. Don’t ever wire money: Only scammers demand it. And “for God’s sake,” don’t e-mail your credit card numbers.