Go down into the Paris METRO and you will hear musicians of all sorts playing music of all sorts.  They play for whatever coins passers-by will drop into their bouzouki cases, and I suspect some of them make a pretty good living.  But not-just-anybody can set up their marimbas in the METRO.  In order to avoid cacophony and fist fights, the directors of the METRO have partitioned this potential war zone.  Each musician has a territory.  You get your territory by applying to the METRO for permission to play and you audition before the directors and if the directors like your music you are granted leave to play underground.  Some musicians' territory is actually on the train itself as shown here.  After playing a 'set' they pass through the car with a bucket collecting donations.
One of the advantages of this sort of work is that the income is virtually impossible to prove and thus is effectively tax-free.  France's tax-rates are what we would call 'confiscatory'.  Cheating on your tax return has become an art-form, and here we see real artists doing it :-)
Want to hear more about the Paris METRO?