I've been using https://www.fakespot.com to flag bullshit reviews for a few months now. After many happy purchases informed by its review analysis, I believe it works.
It's impossible to validate. Further for all we know Fakespot (which curiously has been mentioned multiple times) might itself be a fake that undermines products that are sponsored, etc. It probably isn't, I'm just saying.
? You could manually analyze the reviewers for suspicious non-specificity, typical of paid reviewers for whom it is not cost effective to write a tailored review when they are being paid pennies per post.
Also over time you could compare the quality of products that it says have fake reviews vs ones it says does not.
That's why I'm launching my new website, SpotFakeFakeSpot, which helps spot fake fake review spotting sites. I got the idea from my time as a sales rep selling radar detector detectors to police departments.
Would be amazing if fakespot runs the whole fake review business and therefore can tell you which ones are fake. Wait until this becomes a paid service.
Probably not, though, so more likely the fake reviewers will find a way to avoid its detection algorithm at some point.