Yes, I don't usually leave feedback for a cancellation but if it's several times in a row or more times than I've seen the guy, then yes I would be keeping the booking form and leaving neutral then if it continued, negative. I'd say something to the effect that I'd seen him, he was fine in the booking but had since become unreliable.

Quite a lot of guys on AW do continue to gain positive feedback, whilst double booking and messing others around.

I would leave a neutral and then block him on Adultwork so he can't book you there again.I certainly would not book him in again and would have blocked him after the 2nd cancellation in a row.

Yes leave a neutral with a polite way of saying he has cancelled so many times so others are aware
I have never worried about getting bad feedback in return as anyone can see from the date and time feedback was left that it would be done in spite if they did leave one after.  Plus I feel if someone deserves a negative or neutral then its only fair to warn others

I had one over the past year who books two hours then cancels at the time he should be there and kept getting new profiles to do it.  So I have left negative on all his profiles so others are aware of what he does as he started off as a good client