If you paid via Paypal funds, you can do a chargeback for non delivery if you file with 30 days. They only return what they are able to recover from the seller's PayPal account.
If you via PayPal by charging it to a credit card, you can do a chargeback though your CC company and get a full refund for non delivery without Paypals help or approval.
If you paid via check/money order, you are screwed. This website:
http://www.mindspring.com/%7Ebookdealers/ripoff.html will tell you steps you can take to file criminal complaints against non performing sellers.