I didn't answer the question with laws in mind, as the parent wasn't exactly asking a legal question, but what I would guess would be more a moral one.

IINAL, but since we are at the topic of laws, in the last years influencers (at least in Germany) had to fear hefty fines if they didn't label sponsored posts as such, as that counts for covert advertising. As astroturfing could be construed as advertising, that might fall under the same law.