Extortion makes no sense. Clubs are commercial venues. Everything that personnel extortions comes straight from owners' pocket. So they have huge incentive to figure it out, and I personally haven't experienced that kind of thing.
Extortion doesn't come from owner's pockets. That money comes from guests who want to enter the club but won't be able to do so unless they pay.
I always say: Tell me who you work as and I will tell you how you make "left" money.
Every guest who chooses to not participate won't spend money at the club. Every guest who chooses to participate will now spend less money at the club. If you're the club owner you'll definitely make sure that paying customers' entrance to the venue is unobstructed.