Combat paintball in Thetford mix punters & own guns and honestly doesn't cause any issues that I've seen yet.
Own gunners tend to hold back by playing semi auto/conserving paint and act as a good leader that people actually listen to (he has an awesome gun he must know what he' doing right?!)
Punters like having someone that has some experience to share and so far seem to love seeing what else is available instead of the rental guns, especially when you have some mil-sim guys roll up in full kit.
This site does do a good job of keeping the teams even in my experience, not sure if others do so well on this.
My first time paintballing was actually as a rental against a group of own-gunners and I didn't feel put off at all, it encouraged me to be more competitive and also to later go on and gear up myself.