IF YOU BUY MULTIPLE ITEMS ON BUY IT NOW. TRY THIS FOR SHIPPING TOTAL PURPOSES:

When you go to the cart to pay in ebay you will see all the items from a single store (e.g. yours) one below the other, at the top of the first item there  is a link  that says REQUEST TOTAL. IF you click on this, it links all the item together and then send the REQUEST for an invoice to the seller. 

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To issue a combined invoice from Seller Hub:

Go to Orders.

Check the box beside any orders that need to be combined.

Select Send Invoice for any of the orders selected.