last minute cancellations and no shows are just one of those things we have to put up with in our job. You will never eradicate them completely but there are ways you can keep them to a minimum.
Firstly, on my client record card, in the declaration that the customer signs it says they need to give 24 hours notice for cancellations or a cancellation fee may apply, and that if they fail to attend appointments without giving notice they may be charged the full price of the treatments they had booked. In practice though, what I do is this:
Send people a text the day before to confirm their appointments.
With a no show, I ring them. If they apologise, re-book etc I overlook it. If its clear they have just messed me around, I will not re-book them unless they pay a non refundable deposit up front. If this puts them off booking I dont care, if they genuinely wanted the appointment they wouldnt mind paying the deposit.
With late cancellations, I'm flexible, if its for a genuine reason like illness I accommodate them as much as I possibly can. If they are just messing me around I give them a warning that if it happens again I will have to charge them a late cancellation fee. If they then mess me around again I charge them 50% of whatever treatments they had booked and they have to pay this before they can book again. Same thing here too, if that puts them off re-booking I dont care, I'd rather they left the space in my appointment book for someone who's going to turn up to their appointments.
In practice I think I've been lucky, I've actually only ever had two clients who I've had to apply charges to for messing me around, the vast majority were genuine problems or oversights, and by just accepting these things as all part of the job, I've helped many clients and they have remained happy loyal clients because of it.
All that said, it doesnt make it any less frustrating when you have weeks where all you seem to get is no shows and cancellations! Just take it on the chin and carry on.
