After seeing all the problems people have with trading via PayPal and CreditCards, I'm wondering how the scammers operate.
Are most of them using stolen cards/accounts, or are most of them people using their own accounts to be major douches?
The reason I ask is because this would make a major difference in how you go about trying to prevent scamming.
Both. Pretty easy to get buy a list of thousands of compromised account numbers. Some scams are even part of organized crime.
The other side of the problem exists too. It is called "friendly fraud" but there is nothing friendly about it. Given the amount of real credit card fraud pretty easy for someone to claim they didn't order X especially for products which don't have physical delivery.