I have had great success with eBay, and very little hassle, and I only accept USPS money orders, or I wait till checks clear before shipping.
It's all about trust - sometimes you get burned, but if you communicate with the other party, and the deal is fair and logical ..... your odds for success are as good as any other merchant.
I even mailed a keyboard to a guy before i got his payment. That was an exception, but I had a good feeling about it, and I wanted to believe in people. Sometimes you get let down, but it's better than not trusting at all. If you use your head, and stay away from "amazing deals" that are rarely legit .... you'll be ok most of the time.