Tbh, all you have to do to ensure a day that will be as hassle free as possible is to interact with the customers in as friendly a way as possible, right from the off. Granted you will get the odd knobbers who want to do their own thier own thing but so long as you demonstrate the potential for injury, and what a paintball to the eye can actually do, they tend to listen and actually apologise for any misdemeanours. I used to show them the scar on my left eyeball (believe me, I've taken one, and it scares the facking life out of you, not to mention hurts 10 times worse than a kick in the swingers). Although can I stress the incident was genuinely NOT my fault or the site owners, just the one dick who likes to spoil the session.
It can also help calm people's nerves if you can incorporate a little humour into the safety brief at the same time. Remember you are gonna be part of a group of say, 6 refs, who are gonna have to control a group of approx. 50 testosterone filled trigger happy loons, who are there to spend their hard earned, or ill gotten whichever way you look at it, and they just wanna enjoy themselves and go away knackered and loving the experience.
Personally speaking, to shoot customers from the sidelines if you are not a "terminator or predator" is a bad move and will only help to fuel aformentioned knobber's adrenaline, so you should NEVER do it as a ref.
Oh one more thing, THEY ARE PAYING YOUR WAGES NOT THE SITE OPERATOR