I have an assistant who handles nearly all scheduling and administration for me, personal and work.
We sometimes run into trouble when a new medical/dental office says, "I'm sorry, I can't talk to you, I need to talk to the patient." This means me calling, waiting on hold, transferring to the correct line...I'm sure you're familiar with the US healthcare system. Sometimes they won't even accept when I say that my assistant speaks for me. Even when they do, it's a hassle for every new provider.
How does one authorize them? I have trouble imagining Jeff Bezos schedules his own colonoscopies.