I don't think it's one size fits all. I moderate a niche hobby subreddit and we have been fighting astroturfing for years now. We're over 5,000 subscribers but this has been a problem for the mod team since we were around 1,500 or so.

I actually think if we were larger we'd have more subscribers who even knew what astroturfing is, how to spot it, and why it's important to shut it down.