I mostly list Seller Pays - so that link works for me. Though I have yet
to see any refunds. I use Buyer Pays for low value stuff, so that the
buyer can easily see that postage can (or rather could) be combined. A
buyer needs to order all the items at the same time to get the discount
under EBAY, but I used to be able to allow them to add more items to the
same packet (before posting) by refunding them the postage element
immediately.

SD just takes away any means to meet customer's varied needs.