If it's true astroturfing then it is by definition a professional operation. Astroturfing has to be directed by an institutional authority, otherwise it actually is grassroots.
Single-purpose accounts driving an agenda in a deceptive way aren't necessarily institutional. Normally I wouldn't quibble about definitions, but since I used the word astroturfing above, I want to emphasize that I'm not saying they work for Google. We don't know that, and for HN anti-abuse purposes, it doesn't matter.
They could work for a law firm or some other subcontractor of Google without Google actually knowing about it.