All costs, such as shipping, can be deducted as long as you file a
schedule C. The problem is that the casual seller now has to declare
them a self-employed business in order to file it. That brings up a
whole lot of other issues and costs; FICA, etc
I think Ebay pre-loads free shipping because that is what it keeps
hawking. I've had several times when I did not specify free shipping but
it listed that way anyway. You have to be constantly on guard with the
way ebay manipulates your sales listing...