You cannot give a buyer negative feedback.

Don’t let the case get to the point of eBay resolving it in your absence of your own action. That’s the worst outcome for you.

Read this: https://www.ebay.com.au/help/selling/managing-returns-refunds/ask-ebay-to-step-in?id=4702

❝Whenever possible, we recommend resolving your buyer's issue and not asking eBay to step in. If it's counted as a case closed without seller resolution, it may affect your seller performance level.❞

❝If eBay steps in to help with a return at any stage and the buyer returns the item used or damaged, you'll no longer be able to deduct an amount from the buyer's refund, even if you qualify under our seller protections.❞

Also read this: https://www.ebay.com.au/help/policies/selling-policies/seller-protections?id=4345

And this: https://www.ebay.com.au/help/policies/selling-policies/payment-dispute-seller-protections?id=5293

And this: https://www.ebay.com.au/help/policies/member-behavior-policies/condition-returned-items-policy?id=47...

If you have photos of all that was sent by you, those should be used if you accept the return and deduct an appropriate amount for what isn’t returned to you.

You can report the buyer for abusive behaviour if you believe they have indeed abused eBay policy with a false claim.