But if the buyer initiates a charge back through his creditcard company, Paypal will side with buyer?
If the Seller has done business in a way that meets the criterion of PayPal's seller protection, PayPal will guarantee the seller against any non-delivery charge back. Mail order people have all sorts of measures to protect them selves against "items significantly different" scams, but yeah you are at risk as a seller. Bear in mind that the scammer is committing fraud, and mail fraud in my case (please folks keep this in mind when you are repping FedEx or UPS) and that's felony stuff, and to win their claim they will be subject to some investigation, but yes. This is one exposure that is covered in my insurance policy and I've never had a claim in 12 years as a seller. There's easier and less punishing ways to steal.
Kevin