You can't tell if it's really against their wincon until it's too late. Plus replacing them would give away their affiliation. If they do it multiple times then blacklist them
I can only think of a couple times on DDO/DART history where someone was blacklisted.
1. Royalpaladin, not for playing contrary to her win con, but for getting into insanely personal attacks at the slightest mention that she was scum. She would do the forum equivalent of burning your house down in response to the slightest pressure and eventually it got to much for people and she was blacklisted.
2. Mharman after throwing a mafia game for his team when he was pissed he got lynched.
Mikal was definitely in the wrong for what he did. I debated with him about it yesterday in discord and told him how dumb he was for doing it, and his response is that he basically thought he was done for and there was no escaping a lynch. I told him why that was dumb but I don't think he gets it. And he's occasionally aggrivated people in live mafia with similar plays, but he doesn't consistently do it, and randomly will play normal like he did in drafters game. Though I am sure if he continues to do stuff like that either people will stop wanting to play in games with him, or he will start getting policy lynched until the behavior is fixed.