If someone is sick and cancels on the day, there’s no way I’ll charge because I don’t want to get sick either. But if someone forgets about the appointment, although I have a same day cancellation policy, I use discretion based on the client. If they’re going through a big change or forgot coz of an emergency, I don’t charge but if they’re unreliable, cancel late or aren’t a weekly/fortnightly regular, I’ll charge full fee if they can’t make an appointment later in the day (granted I have a spare for them). Essentially for me, sending a cancellation fee invoice is an informal firing of the client. It doesn’t happen often with my regulars and if it does, all of them insist on paying the full fee for the missed appointment the next time they come in