There is a general principle, that a metric which is used to determine [important decisions, e.g. pay, promotion, sales, etc.] will soon cease to be a reliable

There is a general principle, that a metric which is used to determine [important decisions, e.g. pay, promotion, sales, etc.] will soon cease to be a reliable metric. If your neighbor tells you that a product is good, they probably really think that, because not enough people go to your neighbor to ask their opinion, to be worth spending $$ to change your neighbor's opinion. Amazon ratings, quite a long time ago, became way to influential to be a reliable metric, because the incentives to game it or outright pay for a better rating are too high. Oddly, by aggregating many opinions just like your neighbor, it becomes LESS reliable than if it were just a single data point.