2 it's an open forum. You always engage them in public. Maybe the troll replied in a fallacious way that caused someone else (a viewer) to think they had 'won' (i.e. made a good point), by replying until they reduce themselves to the nonsense at the bare bones of their argument. You may enlighten others to their tactics.
3. You compare troll battles to chess. Well, If another person breaks the chess rules, they are disqualified. They don't win, the people watching the chess match don't think the guy who cheated 'won', he is ostracized. If the aim of a troll is to cause confusion and spread lies (which they can do, as the rules of engagement are totally different and open-ended compared to a chess match), you spray them with the truth. Which is important because as I mentioned before, it's a public forum.
A little tip, if you want reasoning, ask. Be curious. Don't do this weak dancing around the point trying to put me in a box as someone who just thinks out loud when we've never communicated before.