Paul, I believe the rating system is accurate. If Tom gives them a rating of 1 and others that have had a positive experience give a rating of 8 to 10, that doesn't mean that ALL of John's cars are bad.
Tom's rating will lower the overall score by a small percentage point but that doesn't mean that the overall score should drop to Tom's rating.
What tends to happen on internet bulletin boards is the Lynch Mob mentality. If one respected person complains than a lot of people jump on the band wagon. This will keep going until someone shows up with a rope at the nearest tree.
I've seen this too many times on BB's and it may not be fair to John or to the other satisified customers that own a JPS.
Remember, you're only hearing one side of the story.
In conclusion, I'm not calling Tom a liar, only pointing out that no one has heard John's side of the story.