If you're not happy with the price you got for the item then the next time you list something for sale decide how much you want for the item, then add on a bit more to the starting price or Buy It Now price, depending on whether you're selling using the Auction or Buy It Now format. Make sure that the extra amount that you add to the actual price that you want for the item is enough to ensure that you acually get the amount that you wanted for the item, even after eBay (and PayPal, if you have not yet been switched to eBay Managed Payments) have taken their cut of the final selling price. If you do that then you should end up with an amount for the item that you'd be happy with and will not end up feeling as though you've been ripped off.
