Best regards,
First, you will have to wait for ALL items to be paid for AND hope that happens within your Handling time before you ship.
The eBay cart "should" have a function whereby the Buyer can Request an updated invoice, when they do that you simply combine things, lower the shipping cost and send off the invoice. Then there is no post purchase refunding.
That of course may not happen so here is how you can Combine shipping on separate Paid items.
On the Awaiting shipment - print label file use the check boxes on the left for JUST the items that Buyer purchased. Then go to the top of the list and use the pull-down menu and select Print shipping labels.
The next page is the bulk label page and you use the check boxes on the items on the left then the Combine button at the top of the page. You adjust shipping method, weight and dimensions and a new amount will appear int he upper right of the page AND you can look over on the left to see the Total the Buyer paid. With those two numbers you can see how much you need to refund.
Print the label. If you want a receipt it is a secondary print function.
Next, go to your See all orders page, find the transactions and decide if you will refund the shipping overage on one or all of the items separately ... I usually just do it on one. Use the pull-down menu on the left and scroll down to Send refund, click that. On the next page you use the pull-down menu at the top and click Shipping discount at the bottom of the list. Then type a message explaining that you combined shipping and are refunding on the transaction. Enter the amount in the field at the bottom then cycle through completion below that.
