Planet Money did an episode (https://www.npr.org/sections/money/2018/06/27/623990036/epis...) about fake reviews and talked with the creator of ReviewMeta (https://reviewmeta.com/), which attempts to distinguish real reviews from fake ones based on things like similarity and clustered posting.

Of course, if it has or gets traction, fake reviewers will adapt, just like spammers do.