Buying multiple items from one seller + combined shipping

[jaroslaw_ejsymont]

Hello, I would like to buy more than one item from a seller and get one shipping charge for all rather than each shipping summed.
I added multiple items to my cart and would like to get an invoice from the seller (top right button on "Your eBay Shopping Cart").
I click "Request total from seller" button, go to next page and click "Commit to buy & submit request" button.
And then I get "The seller does not offer combined shipping discounts.The seller has disallowed combined payments and shipping discounts. Please proceed to checkout to complete your purchase."
What should I do to get that or what a seller should "fix" on his side?
Thank you in advance for quick answer.