On the public square or market, the charlatan/doctor would also perform some small surgery or tooth pulling.
"It hurts, we take it out", no other solution in those times, of course, but enough to show how "knowledge" is Magic and Technology and Solutions.
The panel on the back is the Doctor's advertisement "Fama volat" (Reputation Flies), that the doctor uses to be recognized from one market to the other, as his reputation grows.
"Credilo, amico, un pari a me tra cento
Non v'é in quest'arte,
e il dente, che ti duole
Fidati a me fuor tratto in un momento
Mirar godrai con la radice al Sole."
"Believe it, friend, there is nobody as good as me in a hundred, in this craft,
and the tooth that hurts you ...
Trust me that I will take it out in a second and you will feel great
with its root out in the Sun."