IMHO, adding a "rating", either to the SP, the review or the reviewer is not going to add any reliable information. Why? Take Ebay: a huge percentage of the "bad" feedback is totally irrelevent, complaining about transportation dammages and delays, customs fee, brooker fees... All stuff that doesn't relates in any way to the product or store evaluated. The only way to get a real idea of reliability is to read the feedback, not only looking at the rating.
Here with MERB, we're talking about peoples dealing with peoples so, this is even worst: the "ymmv" factor. How can we still make a decision? Reading the reviews! It's not foolproof but it's way better than a rating system. I had so-so sessions with ladies who were reviewed extremely favorably by a majority and I had my best sessions with SP that were reviewed as not that good by some others. A rating is, IMHO, an attempt to "make things easy" but when dealing with peoples, there's no such thing as "easy". Somebody who want to make an enlightened decision better read and form his own advice rather than relying on a number.