I buy and sell on Ebay all the time. It's a great way to get stuff on the cheap. Still, you shouldn't buy or sell expensive items (or whatever you consider 'expensive')--the odds of getting ripped off seem to grow with the cost of the item, and Ebay
will not help you regardless of how many complaints the other person has against them.
Paypal isn't much better. Bank transfers are free, and I never let them hold more than $50 of my money at any time. They have an annoying habit of freezing people's accounts without any explanation or method of recourse.
With over 200 transactions, I've only had problems with one pirate software scammer. $20 down the drain. But it's like the saying goes--you pays your money, you takes your chances.
If you are scammed on ebay, and you have the sellers actual name and address, file a mail fraud complaint. The post office investigates every one of them and they get action!