I have a restocking fee of 20% which for high value items can be quite a bit. So in those cases I'm happy to refund minus only my incurred costs to the buyer if they are polite and reasonable about things.

Unfortunately it seems that eBay gives me no option through their system for a partial refund so I'm going to have to hit the buyer for the fees too. You mention doing a partial refund through Paypal, but I have a vague recollection of getting a defect or something last time I did that.

The other way is to tell the buyer to open a return request, I'm trying to avoid that but maybe it's the only avenue here. Especially in case they select a different option for the reason rather than change of mind.