"Paying rent" is a metaphor for life expenses in general. Whether you want to admit it or not, people need MONEY to live life, period.
And who gives a shit if he has other business? That's not what the debate is about. Even if i managed my best friend of 20 years, i would STILL charge him because time is MONEY. If I spent half the day "managing" someone, that is half a day I could be spending on doin other stuff that would get me paid. See how that works?