Feedback is not what you worry about in circumstances like this.

Giving that person a strike for non payment is the most effective punishment you can give.

After 4 days open an official non payment claim with ebay. Don't even mess around contacting the buyer. Go straight into an ebay claim.

That way you will get your ebay seller fees refunded and the buyer will be given a non payment strike.

No one will see it, not even the buyer, but they will be informed it is there and the ebay system will know it is there and if they get another strike in the near future, they will find themselves blocked from buying from a lot of sellers.

That's you best revenge. Forget feedback, you can only give positive and no way do you want to give a non payer a positive rating, it only boosts their score and makes them look better.

Plus if you try saying anything negative in a positive feedback, you're the one who will be in trouble with ebay. So forget feedback.