@two-sewing-peacocks,
Using the link jen...., gave you will help you set up the combined shipping rules, but will not help you make money on ebay. Starting auctions at a penny is a poor selling strategy. If you are going to add a Buy It Now price to those auctions that is much higher, than the starting price, it can discourage bidding. Many may feel you may not go through with a transaction when the BIN price is much higher than the starting bid. Start looking up item using the Advanced search feature, to see what prices an item is bringing, and to see if more sell as BIN or as auctions. Check the sold auctions to see what the starting prices were. ebay's suggestion to start items at a very low price often does not work.
If some of what you are currently selling is rare, then you need to start the bidding higher. Unless you are using padded envelopes to ship coins in, charging $2.80 is going to be seen as a high shipping cost for standard shipping, and adding $2 per additional item will be a deal breaker in many instances.
Having an across the board combined shipping rule can cause problems as well. Since you sell different types of items, some may be too fragile, or bulky to be combined economically and safely. If a buyer does buy several items over a period of days and doesn't pay, those items can be easily combined. You click on (Send Invoice) on the last item sold, and all of their purchases will be displayed, then it is only a matter of packaging them safely, for shipping. If you calculate shipping you can add a new package size and weight, and the invoice with shipping wil be sent.
You need a digital postal scale, to calculate and combine shipping, but a decent one can be found on this site for around $12. If you may sell heavier items in the future get a scale that will take a heavier weight.
"THERE IS NO SUCH THING AS FOOLPROOF, BECAUSE FOOLS ARE SO DARNED INGENIOUS!" (unknown)
