It happens and like you said it's one of those liabilities we take on a s providers.
Clients take on risks of their own as well.
About implementing the cancel policy:
I like to govern myself in a way that shows mutual respect. We all have things going on. I have a stated cancellation policy on my website that I reiterate when corresponding with clients. I also follow up with clients regularly to reconfirm and encourage them to keep me updated on their schedule. I seldom see multiple clients a day so I try to be flexible on time, and schedule myself to be flexible even when I am seeing multiple clients in a day - that way if a client is running late it may not require an outright cancel but maybe shortening an appt or moving the time. Outside the 24 hour window I am somewhat relaxed about cancels and reschedules. (Granted, I can be this way with my local clients because I am a part time provider, I don't have the same flexibility when on tour)
If you choose to implement a cancel policy, what I will say is that you need to make sure you have processes in place to keep yourself accountable and professional. Don't be the girl with the cancel policy who doesn't follow up in a timely manner, communicate clearly and efficiently, or constantly cancels/no shows/reschedules clients on a whim.
Also may be worth it to consider - If you have to reschedule or cancel, how are you going to accommodate the inconvenience to the client (who maybe shifted his day around, has to go to lengths to disguise the expense on his finances, etc.)?
I know this is a controversial stance to take as a provider- but I do NOT think it's fair to clients and is one-sided to have a cancel policy but not be willing to be accommodating when it comes to having to cancel as a provider.
BUT every provider has the autonomy to run business as they please.
And as many will tell you, it is hard to enforce depending on who you are dealing with. Some people want to see YOU! And understand what a cancel does as far as financial loss when you have to secure a room for incall space and they will pay the cancel fee.
Others will move onto other fish in the sea.
It's all good, either way. Keep being a great provider and the good will outweigh the bad.