I ran into a similar problem last year and Paypal didn't help at all. I was fortunate enough to have used my CC at that time so my CC reversed the transaction and made Paypal take the hit. I think you can do the same if you used your bank account as a source, so make sure you file a claim with your bank ASAP. DO NOT RELY solely on Paypal, get the ball rolling with the bank coz it may take a few months to resolve. Out of curiosity, what is the sellers feedback rating?
My frustration with PayPal in the past is they try to deceive you into paying with your bank account rather than your credit card. If you've tried switching your payment options on eBay or any other kind of invoice, it take you to a page that asks blatantly "are you sure you rather pay with CC," choose bank transfer because we'll protect you every inch of the way. Of course I'm sure because PayPal always fails you then it points out that you waived your protection guarantee in your user agreement. Lawyers, here's a note on how to make easy money, sue PayPal for manipulating their buttons so that the buyer is coercised into their paper protection. If you noticed, whenever you click a button such as switching your address, after opting for CC payment, the page will revert to bank payment. I know I've talked about PayPal on my soapbox for a long time, but remember the most important lesson is PayPal is beneath the authority of credified CC companies and it knows it. Always choose CC payments if there is no benefit such as a discount for other options.