If the tracking is showing that the item has definitely been delivered and received by the buyer then ask him/her to open an Item Not Recevied case. If the buyer does indeed open an Item Not Received case then as soon as eBay see that the tracking proves that the item was successfully delivered to the address provided on the PayPal confirmation of payment e-mail then the case would be decided in your favour and the buyer would be unable to leave you any feedback in relation to the transaction.
In the event that the buyer leaves you negative feedback prior to losing the case then contact eBay Customer Services once the case has been decided in your favour and ask for the buyer's feedback to be removed, reminding eBay that they decided the case against the buyer, and for that reason the buyer's feedback should not be allowed to remain. If you do that then eBay will remove any negative feedback left for you by the buyer and your feedback history will not have been adversely affected by the feedback left by the buyer.
Finally, if you have not already done so, add the buyer's User ID to your Blocked Bidders List so that he/she cannot purchase anything else from you in the future and cause you any further aggravation.
