I read somewhere that fake reviews are technically illegal in the USA. Reviewers who received a steep discount or for free are supposed to disclose based on some law supposedly- because it may be promotional. Like YouTubers, Twitch streamers, or influencers.

I don't know what law this is but I'm sure if someone ever got angry enough at Amazon and hit them with a massive lawsuit to enforce the fake review problem, Amazon would probably fix it within a few months. Amazon's pretty proactive and they tend to respond best to lawsuits. I follow lawyers for Amazon sellers who sue or threaten to sue Amazon and/or Amazon sellers in the US.