If a buyer is purchasing multiple items from you, and they haven't already benefited from a shipping discount, they can select Request total from seller in their shopping cart. You can then send them an invoice with the new combined costs..
How do I combine shipping costs if I haven't paid yet?
If you order multiple items and haven't yet received a shipping discount, you can select "Request total from seller" in your shopping cart. I can then send you an invoice with the combined shipping costs.