Do have some flexibility with regular customers, the same way we have it with you when it comes to scheduling and cancelling.
I had a masseur that was seeing sometimes 2x per week for a few months. One day I scheduled an appointment and literally was so tired that fall asleep and did not wake up on time. He called me and I apologized, instead of saying no problem, he demanded the full session paid. I did via paypal. And I never hired him again.