Absolute rubbish. Either the seller hasn't a clue or is just being awkward.
Asking is as good a way as any,all seller has to do is go to MORE ACTIONS > Send Payment Details enter revised postage and send the invoice.
If seller cannot understand such a simple procedure, direct him to the answer centre.
Combined Invoices are done all the time, it is not even necessary for a buyer to ask, a good seller would do it automatically.
