Like you said, it is subjective and she may even be uncomfortable.. If you are hesitant about seeing her, wait a couple of months if you wish and see what type of reviews she gets, it may just be that she was having a bad day.. If the majority of reviews are favorable I say go ahead.. Sometimes a few not so good reviews mean that she is a legitimate human being not perfect after all..

If you ask her to provide her side of the story you are putting her between a rock and a hard place. On the one hand she may want to explain her side of the story in order to gain you as a client. On the other hand you are cornering her to essentially bash on the gent who reviewed her and that definitely does not put her in a good position. No one likes to be cornered.

If I read a not-so-good review on a provider and the other 90% of her reviews are good, I figure that guy was most likely the problem and not the provider.  Maybe he wanted to do something that wasn't offered, he was asked to shower first and was offended...something like that.

Now if 1 out of every 5 reviews is not-so-good, then I wouldn't see them.  You just have to use common sense.  Or just don't risk it.  Your call.

I've read one or two unfavorable reviews on ladies I've seen and it makes me scratch my head since I had an awesome session with the same lady.

If there is only one low review per page or more of good reviews, I'll usually discount it.  I look for consistency in the reviews.  Wide swings in reviews is a red flag to me...  either she's only good with some she clicks with OR possibly some are bogus!  A single low review I'll read the whole review...  often their are clues like "She wasn't my type but I saw her anyway".  
Sometimes one can inquire if they had reviews or say you are reading reviews on TER site.  The provider is sometimes anxious to volunteer the info.  If not, I would not push.
As a VIP member you might want to PM the last few clients (often don't get a response) but YOu might get ONE & give you some more info.  NEVER ask or expect any info that would compromise her safety or security.

If she has one rogue review that is not in sync with the majority perhaps look at the other reviews the man wrote. If he has a bunch of negative reviews well maybe he is married to a supermodel.  If his reviews are usually positive well maybe re read that negative review . You could pm the man that wrote the negative review as well.  As far as asking the provider for an explanation; depends on how recent and can you ask without mentioning inappropriate terms.  Maybe tough to answer on her end without crossing into terminology etc that cannot be discussed.  I guess if it were me I would try to answer but would probably wind up being too vague out of necessity to truly explain.  Tough call any way you look at it.  Cc'd