Like Talad stated, we do not interrupt roleplay unless we see something that blatantly goes against the game policies. And like Vonor pointed out, if we are called in to observe something or clarify a misunderstanding, we will do so.
And regarding the case Elady has brought up, we did investigate what happened during that player event and talked to all the parties as well.
Now, here's a reminder:
It is not and will never be against the rules to play evil characters.
It is not against the rules to surprise other players with evil actions like scams. Talking to your targets to avoid OOC problems later is a nice thing to do but it's not mandatory and will not be enforced, just recommended. However, using loopholes and mech limitations to get away with scams without giving the other players a fair chance to win will always cause problems and we are more than likely to be called in. Each situation is different so we can't really issue a policy that will cover them all and not hurt roleplay in the process. Therefore, we look at each case individually and that is how this issue was handled and resolved.
Also, do not hesitate to contact a GM if you have any questions about the rules. Not knowing them is the player's responsibility and does not exempt them from punishment if they break any but we will do our best to clear your doubts if there's anything you don't understand about them.
Now, if you have any doubts regarding GM actions, you are welcome to talk to us about it in IRC: #planeshift-gmtalk.