If he is signed up for the Global Shipping Program, he actually can't combine and discount shipping. (Another failure of this poorly thought through program.)
If he has Immediate Payment Required enabled, he is in the same position.
Ask the seller to bill you directly through Paypal's Send Money service
Paypal has both Buyer and Seller Protection policies in place that are similar to and as strong as eBay's, so both of you can feel confident about the sale.
He should include the eBay transaction numbers in the PP text box. When you pay, he manually marks the purchases as Paid.
Otherwise, he has to bill you the whole amount advertised, you pay it all, and then he refunds you separately. Unless he does the refund in a very particular way, he ends up with a Defect on his selling account, which is again another poorly thought through policy.
