at least six positive reviews by reviewers who themselves have at least six reviews, and they should all be within a two or three year period.

with at least some from experienced reviewers with 6-12 or more reviews themselves.   I will not avoid a provider with isolated low reviews if the balance are consistant.  And this is by READING the FULL REVIEW, not just going by the numbers which is too arbitrary.   So much depends on what the client is looking for.  
I AVOID providers who show wide swings on a regular basic...  either her service is inconsistant, only does well with clients she clicks with (and face it I'm no longer super stud), or she is plain moody.  In any case, too much of a gamble for me.  This is time to look at the lowest common denominator, not the highest (Do you feel lucky today?  I didn't win the lottery...  
It really is not complicated.
skb

If your in a major area with lots of provider and reviewer action, some will say 6 to 10 as a minimum. If your in an area with a lot less coverage by TER it may be hard to find ladies with 3 or more reviews. More importantly is who is doing the reviews. When I started I not only read the first page of reviews for the provider, but then read the reviewers first page of reviews. First I might see someone else I missed but I also got to know the local reviewers. Then after I saw my first few ladies I rechecked the reviewers and soon I had a list of reviewers that liked the same types I did and who's reviews I trusted. Now if one of these reviewers TOFFT and was the only review for a new lady that would be enough.