4.Crossposting - Any post that is crossposted to several groups should be viewed as suspicious, particularly if unrelated or of opposing perspective. Why would someone do that?

5.Off-topic posting - Often genuine errors, but, if from an 'outsider' they deserve matter-of-fact response; if genuine, a brief apposite response is simply netiquette; if it's a troll post, you have denied it its reward.

6.Repetition of a question or statement is either a troll - or a pedant; either way, treatment as a troll is effective.