Happened to me a few weeks ago. The tech was already at the property waiting. he arrived early to secure parking. This was a rental turnaround and the customer booked 3 weeks in advance.
Custy: "my asst. is having car issues and can't meet u today. we need to reschedule"
Me: "That's fine but you'll have to wait 2 weeks before i can see you again- or you can give me the code for the realtor box"
Custy: "The code is ****"
The next day she booked another appointment with me-- told her it would be a "standby type" --meaning I couldn't give her an exact arrive time and there is a chance I might not make it.-- she took it. Turned out to be a nice, quick filler job for me and she was very happy.