at what point does a provider go from friendly to flaky when having to reschedule? 2,3,4,5,6?

I would say more than once in a few month span. I used to see Misha who is retired a lot. She would flake on me about 60% of the time. But i could not resist her. So after a while I stopped getting the room until she actually showed up......LOL
I would say you put up with as much as you personally want to and would depend how much you like her. I knew she was a flake a lot so I would relish it when she did show up.

But I sure as hell won't  beg to pay for pussy. You know the old saying in baseball "three stirkes, you're out" in mongering I shorten that a bit, two strikes you're out.  San Diego has got some of the best providers in the biz, why in the world would you put up with all that re scheduling. MOVE ON!

Caca happens, but to many times is a a major red flag!

sometimes patience does pay!