ALL professionals within the service industry should have a cancellation policy. Most that do ask for a minimum of 24hrs notice, so that your spot has some hope of being filled if you cannot be there (almost all professionals within the service industry have at least a small handful of clients hoping to swoop up that cancellation, with enough notice). If you do not give 24hrs notice, the usual policy is to charge you a portion of, or all of, the fee of your regular service, to be paid before the next service. In my chair, this is the policy.
All my clients know this, have been told this, and are rarely (some, never) late (no one more than 10m; and that's usually due to traffic). There are variations of harshness included in this policy. Some service professionals I know also require prepayment of all services from that point on, to make sure the client doesn't "forget" again. I have yet to do this.
I also have an emergency policy. If it is a TRUE emergency (car accident, death, etc), you get a "pass". I also let my clients have a one-time late/missed appt "pass", with a reminder for next time. But, if you just "forget", especially if it becomes a habit, I will enforce this. I haven't had to give more than a warning to anyone in the 8 1/2 years I've been doing business.
Then, though, there's this problem: what if your client, who's never forgotten before, forgets? Then, when you call & text, doesn't answer. You start to worry because she's in her 70's, that's what happens...
Sure, I *could* charge her... but I think I'll just remind her of my policy this time. One reason is the fact that she was one of my first clients, and I'm not sure I actually ever told her my policy. Another is that I had to be at my studio anyway; I had another client after her that couldn't move her time, and I had a friend of mine meeting me to pick up some things.
So, my plan is: when I put my certificates, calendar, licenses, etc back up on my wall, to make sure front & center (visually) are a short list of rules (including everyone washing their hands -- still get some flack about this one -- and my cancellation policy). I will also make sure those rules are included on my brochure, and will inform all new clients when they make their first appt with me.