As far as drop catching and backorders, they are a part of my business and are expenses. Now, if you are not in business, that may be a different story. If it is a hobby, you are not able to deducted expenses like you can when you are in business. Is the states, the only thing you need to start a business is a checking account with you business name on it, that is it. That would be a sole proprietorship which you use your personal tax return to claim your taxes.
With that said, it depends directly if you are running a business or not. I claim all my drop catches and backordering, it is a part of the business. As far as your example, the quesiton is, are you running a business or a hobby that makes money? It you run a business, you made zero profit (1000 expenses, 1000 revenue). If it is a hobby for money, you pay 900 in capital gains. (sold a domain for 1000 which you invested 100). I beleive those are your only two options in you senario.
This does beg to ask a question which just hit me, is Paypal concidered a checking account for purposes of running a business? I will look into that for further discussion this week.