There is really nothing you can do about that except just take the loss.
Always send an item with tracking info because it states in Paypals T+C the seller wont be protected without proof of delivery.
Put the buyer into your blocked buyer list. Then write out a formal complaint to eBay and make the complaint.
Then go to the item page and click on feedback and the seller is given some choices choose the one you like and file another complaint from there.
Then write the buyer and tell him what you have done. Then email Paypal and tell them what you have done.
Thats about it.
If you are finding that your sales or problem sales are coming from low feedback buyers you can state in bold in your listings that you wont sell to people with FB under 5 or 10. If someone with under your prescribed FB buys from you just refund the money and file for a FV refund.