Shit can happen...
I think it's clear that in this hobby, as in most walks of life, shit can happen. Sometimes, the shit is unexpected.
I don't think it's surprising that sometimes appointments have to be cancelled. That applies to SPs as well as clients. In these circumstances, the person cancelling should do their best to give the other as much notice as possible. This is common decency and applies to other business dealings so why not apply it here as well?
If an SP called me to cancel I would take it in stride. If she cancelled on me repeatedly, I might decide to look elsewhere but one or two cancellations over the course of an ongoing association is not a deal-breaker.
As I'm not an SP (obviously), I can only assume that a client cancellation can be frustrating as it represents lost revenue and lost opportunities. I wouldn't blame an SP for declining to book me if I cancelled frequently but I would expect her to understand if it was a rare occurrence and I made every effort to offer her as much warning as I could.
If we expect nothing but perfection all the time, we're all bound to be disappointed.
Zog.