Terrible scores for an otherwise highly to very highly-reviewed provider are often just what DJ mentioned: revenge.
There's a recent post on the Chicago board by a lady who received a very terrible 5/3 review: he booked a massage, then asked for GFE FS at the massage rate and in exchange he'd give her an outstanding review. She declined, and so he gave her a bad review.
My very first review was a terrible one: I never even met the guy; he had an ax to grind with the agency I worked for at the time. Actually, the review was posted just a day after my profile was added to the agency's site, BEFORE I'd ever seen any clients. Obviously fake. The agency owner tried in vain to get it removed but it's still there. He left equally terrible reviews for all the ladies working for her at the time.
Recently, I had a client who, after reading a since-removed false review, thought that I perform acts which I do not... since he was disappointed, he left me a 7. While not terrible, it did drag down my average.
Another gentleman who once gave me 7s thought I'd be happy with his review and was surprised I wasn't grateful; turns out he's just a very stingy scorer, who gave those same scores to a lady who usually gets 9s and 10s for performance. So when you spot a review with scores below that lady's average, take a look at that reviewer's other reviews. In addition to the possibility that he uses his own grading system and not TER's, it could also be the case that the low-scored review is for someone much different than the type he usually sees.
But I know that to a lot of men who do their homework and read many reviews, the so/so scores like I mentioned provide balance, and give a good idea of what might be the worst to expect with that particular lady.
Please keep in mind that we providers are accustomed to entertaining gentlemen of all physical types and descriptions. Thus, we are very good at "going through the motions" with apparent enthusiasm and pleasure, and will absolutely give it our full effort. It's the jerks who refuse to be nice despite all our efforts, who might get less than our best.
xox