Since I kinda started it in the other thread, I have to say that I very clearly stated the possible reason for red trust:
I don't think that would be abuse and it's specific to that situation, not a generic "red trust for commenting on a dispute" scenario. Keep in mind that a big part of the reason why the parties agreed to mediation is because they want to resolve the trust flag and put an end to it. Continuing to escalate it after it's been resolved (e.g. continuing to support the [obviously invalid at that point] flag, or continuing to claim it's a scam) - that'd be abuse of the trust system and malicious behavior.
I know the concept of binding mediation is alien to this forum because we want to keep trolling the shit out of every dispute, and that will probably preclude any such mediation from taking place in the future, but it is really simple. When a dispute is brought up for public debate - fair game. When mediation is agreed upon by the involved parties - the case is no longer up for public debate. We can't really prevent people from being assholes about it, but continuing to make accusations would be equivalent to simply making shit up out of the blue.
So ultimately it's about how you treat false accusations. Most of the time I would agree that a neutral is enough. But mediation is such a clear-cut scenario that I can't think of a non-malicious reason to continue making accusations. If you do - please enlighten