While driving around the city, you may spot red vehicles in your mini map. You have to kill these patrons but you have to be careful since they have several armed guards. It’s better to disable their vehicle first by blowing up the tires then cycle the target until you can target and shoot the patron. However, unless you’re using armored vehicles, don’t stay behind that vehicle because it may explode in a gunfight. Take note that you may also have to deal with witnesses and police so use your Associates as necessary to pull this off.
This objective may deal a lot of damage to the racket but there's no good amount of cash you can collect. It is also too much of a hassle to pull off so consider doing this only when you're still a few amount's short of completely damaging the racket.