I was completely worried about pricing. I haven't had a sale, only been going for couple weeks, so not at all sure what invoices look like, if you can adjust them for postage, etc. I used the shipping profile feature. Found it long winded but once it's done, it's done. I also read that with PayPal, you can refund with no added cost. So if you feel customer has overpaid by the time you get to the post office, that's an option. Good luck.