How do you combine items using buy it now and give a shipping discount.

You set the rules for combined shipping and promotion discounts at ebay in your Site Preferences. You Sync those rules to Auctiva to apply to listings using the "Update Combined Shipping Discounts From eBay" selection in your eBay account settings at Auctiva. Use of Combined Shipping and Promotion rules are then selected on the Auctiva one-page lister in the Shipping Tools section.

Danno

Edit: And, if you need to do one on-the-fly, you issue a Combined Invoice from ebay for the multiple purchases and do the adjustment for correct shipping on the Invoice.