Yes and yes (presuming the items are all Auctions).
Let the buyer know that you WILL provide discounted shipping if they win multiple auctions. When they are finished bidding you can sent an invoice combining the items and you can adjust the shipping to whatever you have agreed upon.
You can also include any Fixed Price listings if the buyer has not yet paid for them (eBay may force them to pay for those separately). Even if that happens you can still adjust the shipping charge on the unpaid Auctions and take into account any Fixed price where full rate shipping has been paid.
Paranoia strikes deep
Into your life it will creep
