I have a book not list, but they really have to be "bad" to get on there.
I think it all depends on the situation and how they handle it. I have actually put one more on there today (not that I have a lot) she had booked in for several treatments, was explained about cancelling rules, was sen a text yesteray and still did not call me to cancel. When I called her she didn't even say sorry, she just said "oh I forgot and now I don't have a car and cannot come to you, so I will cancel" the treatmens was half my day, so lost a heck of a lot of money (she will get a bill in the mail, but probably won't pay).
She will be able to get at treatment if she walks in and I have an apointment open, but will not be able to book one. Others I have banned if they keep cancelling the day before and moving the app. but they are warned first. Then there are those who stay away, never call and don't answer when I call, they are banned right away.
So notice that they are only banned from booking an appointment (unless they pay in advance and know that they won't get the money back if they move it too late or stay away), never banned from treatments, but it is almost the same as I rarely have free slots, but it does sound a lot nicer to say "I am not able to book a slot for you as I cannot be sure you come in, but you are very welcome to stop by when you have the time and check if I have a free slot"
I even have a lady who got the treatment said she forgot her wallet (even gave her food) and never saw her again, I will treat her if she pays what she owes and pay in advance for the treatment before it is carrie out.