That's why I think just leave things for now. The buyer has 30 days from the date of delivery to open a case. You started the thread on the 25 November, so the buyer has less than 10 days remaining.

As I say, Ebay has no reason to do anything, because there is no case in the system for them to look at.

Buyers can only get positive feedback (so it's meaningless) but behind the scenes, some try to negotiate a more favourable outcome. We see it fairly regularly in the boards.

Also, if the buyer tries to extort a refund by threatening to leave negative feedback, this can be used against them in any communication with customer service, especially to have said feedback removed.