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The key here, post when you are highly knowledgeable or even experienced about the topic, but if you’re not, don’t act as if you know it but just skip on it, but learn from it as well.
That part where you advised that people should contribute only to discussions they're conversant with and not pretend about it if they didn't know anything there, it's a good one. However, sticking to that will be really difficult for members who want to cover many sections of the forum so as to meet up with spreading out their posts so they can get their weekly pay from their various campaigns. At the end, they spam there rather than make meaningful contributions.
I see your point there, that is why before trying to engage in a healthy discussion in the forum, familiarize first the different boards and study their list of threads. DYOR if needed because that will open up more valid concepts and insights that will help you out in the forum discussion. With that, spamming will be avoided and you end up contributing well in the discussion.