I think there is some merit here, and possibly a way to take subjectiveness out of the ratings. Use verifiable attributes rather than unverified actions. Instead of “shopped” say “functionality is at 100%”. I guess my point is this is a good start.
Why not have an acceptable standard? If I claim to be selling an 8, and you as a buyer can point to something that doesn’t conform to it being graded as an 8, you now have leverage for a lower offer. Just my two bits.