If we talk about that if someone posts too quickly than he might be spamming the forum with low quality posts, it looks reasonable.
Mostly if a poster makes some posts within a short time, it can be spam posts which are more likely low quality. However and fortunately, it is not always true.
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Right, and that's why my second sentence was about whom to check and not whom to blame. If someone posts usually too quickly it can be a reason to check his posts. If posts are okay it is not a problem by itself. It is just a possible marker of a probability of a problem. But it should definitely not be a recomendation how to comminicate on the forum; while in the boundaries of the rules the one can post the way he wishes.