GM's have almost complete Autonomy when it comes to their RP's, as long as they stay within the overall guild rules. You may prohibit someone from your RPs, you may make your own set of rules for within your RP (as long as they don't clash with the site's rules) etc. If you are going to ban someone from your RP I would suggest you do so with discretion and a little class. Don't make it rule #8 that so and so can't join (not fonz cool) but if they post in your RP, simply PM them and tell them they are not welcome and why. Easy and hopefully, drama free. Good luck.