The 5 stars are basically baseline if the product is good enough for the price it's sold at. Giving anything besides a 5 star is a massive FU to the vendor, as dropping below 4 is basically a death sentence for the listing. That can be warranted for sure, but only if there was something very wrong.
The biggest issue I'd see with your approach is how hard it's going to be to separate bots talking to each other from actual people writing these messages.
Most research on the matter seems to conclude that anything between 25 and 70% are written by bots.
The high range is because it's actually quite hard to confidently assess wherever a message is written by a human. Surprisingly not because it's hard to classify bots, but because people often write borderline incoherent messages too.