You are never going to stop the occasional player "guesting" down a level, this has gone on in paintball for as long as I can remember. You'll often find that a team is suddenly short a player at the last moment through no fault of their own, and the only available player wanting a game happens to be ranked higher than that team. So what do you do - tell them they have to play with only 5 or 6 (in a 7 man), or let them use a guest? Of course it's a different matter when there's so many guests they might as well be a higher ranked team playing under a different name (as I've seen in the past). But in cases like the Control Freaks last Sunday, they still only came 4th (out of 7, 5th if you include Tricky's scores) playing a Pro.
Another thing is - how on earth do you prevent it? It so happens that I know most of the guys from the northern circuit who were playing on Sunday, but how many of you know all the members of Imperial by sight? Or teams like Inferno, K2, Chameleons, Viper or even Kellys? Half of you wouldn't recognise most of the top pro players from just a couple of years ago, so if someone like Marcus Davis came & guested for a Div 4 team I doubt more than 5 or 6 players in that whole group would know who he is & how good he used to be.