MHP I hear what you are saying but in point of fact (site rules), once a booking has been agreed, a review can be left. I don't mix AW with UKP for the same reasons you mentioned.
In this case, due to her apparently lying to me for the reason for the cancellation (saying she was out of London when her Green light was still on and showing her at E14 before, during and after the agreed time) and not repying to further messages asking if this was incorrect (or for her to just tell me the real reason for cancellation and if we could reschedule) I rated it as a negative.
How you or others deal with business is your choice, my review remains a negative for the reasons stated. Neither she nor anyone else knows how much or little inconvenience this caused me - the point is, she's a service provider and when you get mucked about by any person or business you are paying to provide a service, it becomes the tail wagging the dog. Not a good road to go down in my opinion.
All that said, she looks hot as fuck so I do hope others have better luck than I did.