In a post on a different topic, @papso22 wrote I expect it won't be long before ebay stops these refunds, they want the SD label used, whoever pays for it.  I am pretty sure it wasn't meant to be an opt out mechanism.

I'm inclined to agree.  eBay doesn't want sellers going rogue, and I'm sure they don't want tens of thousands of server transactions to process requests and refund the payments.

Both RM and Evri refund unused labels but I'm guessing the numbers are fairly low.  I don't suppose either entity would appreciate a dramatic increase in refund requests - but maybe eBay can't claim, and just has to swallow the cost.