Reviews are fuzzy measurements that humans interpret as individual,
independent, samples.
When you go to the reviews section, your perception is that these reviews are uncorrelated. Correlated reviews are less meaningful, they provide less data. Most people arriving at a review section, seeing 20 1 star ratings, would presume ratings were independent individuals. If 20 independent reviewers each had a bad experiences. That amount of data is extremely telling of the service.
1 singular review, on the other hand says much less.
Maybe their waiter was bad and was fired later? Maybe that was a bad day for the kitchen or the staff somehow? Maybe the reviewer came in with a negative expectation and was biased somehow. Maybe there was some kind of culture issue?
Reviews arn't measurements, they're fuzzy. And while a party agreeing that they were not treated well is MORE information than a single person, it is no where near the signal strength of 20 individual samples.
In this way. They had significantly more influence than was due. It wasn't fair.