For every service there are very relevant factors about what makes the product good or bad. If you don't separate these 2 or 3 factors, then over time everything becomes a score of 3.6.

In the case of Amazon, the relevant options are:

   1. Likert scale of quality:
       a junk, just don't buy it
       b cheap and works good enough for occassional use
       c higher quality: willing to spend more and you'll get a much better outcome.
       d overpriced

   2. bad shipping, bad vendor, poor customer service

I hate seeing a bad review for a product based on the last item, they're normally outlier issues or whiners and I normally try to filter them out.

In the case of rotten tomatoes it is, again a different set of parameters.