This might've been said already. My apologies, if so (skipped a couple pages).
If you must cancel, then ACTUALLY cancel. Don't go into radio silence 20 minutes out from start time, acting like you can't answer calls and/or texts and shit. Now we're left wondering on the other end. Why aren't you answering the texts? Why aren't you answering the calls? Did you double book and blow us off? Are you stuck in traffic, or what?
For a hobbyist like me, I don't go to plan B until it's quite obvious that plan A just isn't going to happen (this basically means I'm in limbo for like, half an hour or so, trying to find another provider to see. So, ladies, if I contact you on short notice, I'm probably in plan B mode. Forgive me for the urgency in wanting to see you, but odds are at this point I'm like, an hour INTO already being horny

).
Once I've gone to plan B, this means I've lost all faith in plan A. If you're plan A, you have maybe 30 minutes past the appt. time to salvage the situation. No guarantees, of course ( I COULD stop plan B actions, if it's real early in plan B actions...i.e. nothing confirmed with plan B just yet). I know life happens, and don't like to put people on some evil NEVER AGAIN list. But when it happens too many times in a row or too many times in a short proximity, especially given in today's time (with GPS), I start to lose faith in you.