Kinda new to all this and the lingo..thanks

the guide linked at the top of this page

Between the estimated mpg on a new car sticker and the mpg you actually get.  But, that is highly unlikely!

I have often seen this used in reviews where the hobbyist sees a lady who consistently score high in performance.  However, this hobbyist felt that the lady failed to live up to his expectation.  

Let's face it, providers are people too.  She may have had an "off day."  There may have been little, if any chemistry, between the two.  The gent's expectation may have been exaggerated.  (Perhaps he read a review for a 2 or 3 hour appointment which included several rounds of fun and he only booked a short appointment).

In any event, the hobbyist who realizes that their experience may be the exception to the rule, may indicate that YMMV to expain this!