Some might sell themselves taking photographs.
The alternative is to sell yourself making burgers, or answering phones for a fraction of the reward.
Everyone sells something of themselves in exchange for something else they want (like food and a roof over their heads). Those who work 6 days a week slaving on minimum wage are selling far more of themselves than someone who does something they love. If you can work as a photographer for someone else two days a week, and have five days to do your own thing then you're doing better than most and deserve respect...