I have no idea how you would go about doing that. Typically the rating is a person's experience and education. In the world of certifications there usually different levels of certification to let you know how much effort the trainer/coach has put into learning.
I think the most difficult part of a ratings system is removing the human aspect of it. Some clients won't see results because they didn't do anything or put in the work. They will blame the coach. Others will get results and their reports could be mixed. Some will gush and herald your greatness while others will feel you gave what was asked and expected so the rating is average for "meeting expectations".
In Canada they are based on different levels. We have to pass both a theory and practical per level for the sport one wants to coach at. The theory levels carried over, I just had to pass the practical portion for the different sports. For example Level 1, to Level 3. Level 3 is the mininum for coaching National teams I believe. Level 1 and 2 are not that bad to pass. Level 3 gets into the more of nutrition side, mental preparation and injury prevention and treatment. That level gets pretty deep.
This will require so outside-the-box thinking. Community rating is used to rate pretty much anything these days. In my opinion it's a far better measure of competency than traditional measures. Lots of bugs to work out, though...
I think the most difficult part of a ratings system is removing the human aspect of it. Some clients won't see results because they didn't do anything or put in the work. They will blame the coach. Others will get results and their reports could be mixed. Some will gush and herald your greatness while others will feel you gave what was asked and expected so the rating is average for "meeting expectations".
The human aspect also applies to judging the quality of the client's review. If the reviewer can express the positive and negatives in a thoughtful, articulate, and respectful way, then that goes a long way in determining if it's a valid review.
When getting a referral in person, one can ask the former client and ask about their goals, expectations, and background. It's a bit harder when reading reviews.
Amazon has a lot of reviews and a system where helpful reviews are promoted to the top. They also have a system where people can ask questions of the reviewer, too. Not sure if this forum would be technically capable of doing something like that.
Amazon's reviews are open ended, and it is up to the reviewer to structure their reviews. Perhaps having a few distinct sections to help people organize their thoughts on a coach would be helpful, possibly even the reviewer's background. Though, one would prefer to avoid a 50 question survey.
