I hope for his own sake that he is keeping good records. A venerable dentist in my own neck of the woods, now sadly deceased, was similarly seeing a large proportion of his less well-off customers for free.
Then one day, a Revenue Inspector confronted him having literally sat outside his door for days on end counting the numbers of customers coming in and out.
The Inspector wouldn't believe the dentist was seeing people for free so he threatened to raise a huge tax demand on the dentist.
So the dentist literally shut his doors. For good.
And the poor people of Co. Cavan lost the only dentist who would cheerfully treat them even if they couldn't afford to pay.