In Chicago's Southside (And Other Places), Auto Mechanics (Who Work

In Chicago's Southside (and other places) , auto mechanics (who work outside the formal sector, without a business license, advertising, or even a garage) will do work for gang members without charging them. In exchange, gang members chase away other mechanics who wish to operate in the area. These auto mechanics have monopoly power; what type of source does it come from?

A) barriers to entry
B) hard to duplicate inputs
C) innovation
D) economies of scale