It's simple: genuine kooks generally stay in their bubble echo chamber, talking with at least vaguely like-minded individuals. Trolls on the other hand regularly go out and share their "opinions" in places where they will be the most controversial. So if you see somebody with an extreme "opinion" talking a lot with people with opinions way on the other side, they're probably a troll, and if they're talking mainly with people with agreeable opinions, they're probably serious.
Trolls are people who either are faking their opinion to stir up some trouble or they are people who truly believe these things but still lash out wrongly. So whether they believe it or not if they start verbally abusing a person or opinion at the wrong time and place, or do it too much or are too harsh, etc. they are a troll.
Those that stay in their "bubble" so to speak are usually the ignorant people that don't like their concepts tested against reality.
Those who continually go out and test the opinions of the opposing concepts are the genuine, more intelligent people who are continually checking their concepts against those of the opposition to ensure that their own conceptualization has some sound basis.
Though I admit that some are likely just trolling or proselytizing their beliefs and trying to convert others over to their beliefs, such as a few on DDO that I have encountered. Those are the closed minded narcissistic megalomaniacs of DDO (if reading this, you know who you are?), while the open minded, exploring members are genuinely trying to ascertain as to whether their current concepts have merit and may change their opinions/concepts/beliefs if they are shown not to have merit.