If the provider has several reviews, I look at the reviews in the last six months/year. I throw out the highest and lowest.

Like any other sort of reviews on line I think most of us take the bad ones with a grain of salt. People tend to complain about the bad stuff and never talk about good stuff. I know when I look reviews for a provider I tend to discount the bad ones if they are only one or two and the rest are stellar.

gives itself away as retaliatory just by reading it.   I disreguard such reviews with overwhelming history to the contrary.  
Wise clients don't go by the numbers...  which are arbitrary.  And I expect to see a number range say a 7-8 or 8-9...  for 2 unique individuals make a unique coupling even when one tries to give the same experience.   What gets my attention is WIDE swings..  say a 9 to a 2!!  A single swing like this makes the review suspect, while several makes me wonder if she only does well with ones she clicks with (knowing I'm not Mr Stud anymore, if ever).
Those with some experience, get very good at reading between the lines...  You do want good reviews to be sure but don't get freaky over reasonable variances.

BTW, even if it costs you some money...  for the rare meetings where it's just not going to work.  Even if you've put effort into it already...   I suggest you say you just can't go through with it.  Appologize.  Say how sorry you are.  Get him dressed.  Give him a full refund.  Get him to leave peacefully.  For your happiness & safety.

Best Wishes,
HV