This expression is again from Iceberg Slim's book PIMP - The story of my life.
Here's the section that contains it:
"Anything with a buzz in it was in great demand on campus. A pint of rot gut whiskey brought from seven and a half to ten dollars depending on supply. My roommate had scratch and a Fagin disposition. He was a sharpy from a number-racket family in New York. We made a deal. He would bankroll our venture if I copped the merchandise and sold it."
Background: Iceberg -the main character- got to a college campus where his slick roommate talks him into starting up an illegal bootlegger's business.
So, what does "number-racket family" exactly mean? A well-educated, rich family with high social status? Or a family that forms a frighteningly powerful criminal organization? Anything else?
many thanks in advance...