So I am helping someone sell their sports memorabilia. The main way I accept payment is through PayPal. So I accept their funds, and then send his part to his PayPal and keep the remainder. How do I prove that I am not making all of the money that is being sent to me, as most of it goes to the guy who I'm helping. I just don't want to have to pay taxes on the full amount. I usually will sell about 10-15 items and just send his part to him via PayPal. What should I do to make sure I can prove that is not all of my income?