@farnorthsid
If you are using calculated shipping, just be sure your weights are right and that you have a calculated shipping rule enabled. If so, then eBay shipping calculator will take care of it. For example if using Calculated first class and the item is 2 oz then buying two would cost the same since 4 oz mails for the same amount as 2 oz. However, buying three would be at the 6 oz rate. This should work whether the items are in the same listing or not as long as that are enabled for using a calculated shipping rule.
If you are using flat rate shipping, you should have an additional item amount you can specify as $0 in the listing, but that only applies to the same item. In that case purchasing 3 would cost the same as 2 or 1 or the same item.
Hope this helps.
