You can prove that someone bought something from someone, but if you follow the chain of transmission, it starts with theft from nature, which is common. Ownership is a loan from the common. If the system of private ownership does not contribute to the common good, the loan should cease. Ownership is thus neither a right nor a higher purpose. So what does this mean? Can I steal? No, nothing but some office paper. A tax level sufficient to cover welfare and good working conditions are, on the other hand, two worthy goals. They are at least as important, if not slightly more important, than the profit.