If you really want to save money as a seller on ebay, you need to obtain "top rated" status. Top rated status requires very high detailed seller ratings, stellar feedback rating. You also must ship within 24 hours of payment and accept returns for 14 days.

Why bother? Well, ebay gives you 20% off final auction fees, and over 30% off shipping rates. A pretty tasty discount. I go into and out of top rated status a couple of times a year. I won't get it back until November, due to some newb buyer flaming me on shipping charge (I only charge actual postage, using ebay's shipping calculator, but some buyers want it lower yet). I have 100% positive feedback, but that is not enough.

Sell enough on ebay, and these discounts are very substantial.