For the benefit of my international customers, I am going to explain the eBay Global Shipping process (as I have learned it to be - from previous customers).
eBay Global Shipping takes charge of fees related to customs, taxes (if applicable), and shipping from the Global Shipping Center (in Kentucky, USA) to the destination country. I have no control over this part of the process.
If you are interested in multiple of my listings, and win (at auction) or purchase (fixed price) multiple items, you must wait to pay until you are done making purchases. Global Shipping will combine all your items into one order and calculate the appropriate fees.
If you pay for multiple items separately, I will be forced to ship them separately.
As for the shipping charges I set on my listings, if they are much more than my costs for shipping to the Global Shipping Center, plus international fees and insurance, I can send a partial refund of the overpayment (and have done so previously).
I hope this helps you understand what I can and cannot do in the way of 'combined shipping' on international sales.