Let's say I want to buy a TV from a wholesaler for $9k (this is just an example to better represent this). If I charge customers $10k, I will pay the wholesaler/dropshipper $9k and pocket $1000. The problem is, come tax time, my personal earnings will say that I made $10k, and instead of being taxed on the $1k I made, I'll be taxed for a higher amount. How do collect information in order to prove that I only made $1k in profit? Do I have to register myself as an LLC or corporation?