As I said in one of the recent threads on RM reviews, when judging whether reviews look suspicious or not I use the following criteria:
How long have the reviewers been members? If the reviewers are long- or medium-term RM members then I regard them as legitimate. How many reviews has the reviewer posted? How many different guys has the reviewer reviewed? How many reviews does the escort have and over what period of time?
One tactic to gauge the legitimacy of a review/reviewer is to ask the reviewer for feedback. I've done that and have gotten everything from an essay to a one-word answer. The one-word answer guys usually warm up after some back-and-forth. If they don't reply or reply with very little detail, I question the legitimacy. (Not to them, of course)
In this particular example, I would look at both the positive and negative reviews and apply the criteria above. If the majority of the positive reviews seem legit, I would chalk the one negative review up to a lack of chemistry, an escort who had an off day, an asshole client, or an asshole ex-friend/ex-boyfriend/fellow escort.