It all depends on how much one trusts an online forum. Btw, what is your measure for determining astroturfing on HN versus Reddit? I understand astroturfing happens here to some extent but I am not aware of any social media manager who spends money on astroturfing on HN. In contrast, I have heard (second hand) about social media guys paying for Reddit astroturfing.
But not trusting anything you read is a very convenient way of denying the existence of any complaints. How else would you tell?