Big lesson I just learned from dealing on eBay: calculate correctly ALL shipping charges involved or you'll lose money.
Both my Vampire mugs sold for $5. I added a $1 shipping and handling charge and let the buyer calculate postage based on their location. I, however, forgot to add the cost of the box in which I would ship the mugs, which means that, at the end of the day, out of $14.84 for both mugs, after everyone took their cut and shipping was done with, I only made $7.24, or $3.62 per mug, which is not a lot. Of course, this is hoping that I calculated the parcels' weight correctly!
Not bad, but I can do better. I just rarely use eBay, and normally it's for books, for which the boxes are free. Lesson learned.