There are some people who accept credit cards and may sometimes take credit cards to secure appointments. I don't accept credit cards, nor would I do that. If you do have a credit card on file for a client who continually no-shows, you could possibly use that, so long as you have a signed form where they indicate that they are responsible for any late cancellations.
I have been successful in the past in getting clients to write a check for their missed appointment. These are usually fairly regular clients, who have violated the policy and are well aware that they need to pay. Of course, there are some who I don't receive payment from and never hear from them again. This is fine. My point is to get them to pay up and shape up and if they can't, then I'm fine with them leaving my practice. I will usually give people a first time 'freebie', but if a client no-shows or cancels 20 minutes prior to their first appointment and doesn't seem at all apologetic, then right then and there I remind them of my cancellation policy and tell them that they owe me for the appointment. That's usually the last I hear of them. I did not want them in my practice anyway, as they obviously have no respect for my time.
So, sometimes you can collect and sometimes you can't. Those who value your time will pay and be apologetic. My purpose is not to make money on these clients who cancel late, but rather to make my point very clear that I am a professional and that I have a policy that I expect everyone to adhere to as best they can. It sets the tone for my practice and you will find that people will respect the policy more.
Most of my clients now when they cancel, I know that they absolutely HAVE to. Occasionally, someone will cancel with less than 24 hours notice and will OFFER to pay without me having to ask. And, that's even when they are cancelling because the person has a cold or something like that. Of course, I do not accept their payment then.
I think it's very important to be sure that as the therapist, that you are fair to them too. You must be punctual with your appointments. You must not cancel or no-show on them. If you do happen to make an error of some sort, it's important that they feel that you value their time as well. I have had some times when I have made a scheduling error and in addition to apologizing profusely, I will also give the client their next session at no charge and will sometimes add on additional time or something extra like some hot stones or something like that to make them feel very special.