It is in this message from the Op:

"they invariably find in favour of the buyer and you'll lose everything."

If this happens will eBay official notify the buyer to keep the watch and will refund him?

I have called eBay, explained my concern, they told me if the buyer opens a case against me, escalate to them, they are on my side.

If the end of the day the decision is in favour of the buyer, why eBay has the authority to let him keep my watch without paying, it is not a counterfeit.