Maybe the people who are actually working for themselves are those who do not need people or to satisfy any customer to make profit, example like the traders who do not need to lure customers to their shop like business owners or hotel owners, or taxi owner that need to follow instructions from their clients etc.
No matter which sector you work in, you need others to exist to make profit and that's why you always depend on the market. Even a trader depends on the market sentiment and has to act accordingly to make money. As far as satisfying customers goes, I guess every service provider has to do it.
For me, working for yourself means that whatever you earn is yours and you are your own boss. You decide when to work and when you want to take a day off. Basically freedom of work is a more accurate way of saying it.