Just been having a read through this thread and it seems to me quite a few people are out of order in the way they are criticising the OP.
He had an agreed appointment, the appointment was cancelled, he's entitled to leave a review. Only he knows how he felt about that or how the situation affected him in getting a replacement. He decided it warranted a negative, that is his choice, it isn't up to others to tell him he was harsh or it wasn't justified, that comes across as white knighting or as a fan boy.
Members can only speak for themselves, therefore any comments on this thread should reflect what they would do in a similar situation. Personally I wouldn't post a negative for being cancelled the night before, but that's my choice just as this is the OP's choice and he gets no criticism from me.
As with any review on this site, it's up to the individual to determine the value in it and what effect it would have in them choosing to book or not.
Edit
BTW there's no way in this world I would alter / not review to pander to an SP's wishes and it upset her so it would mean she wouldn't see me. I say it as it is she could like it or not.