This is one of the reasons I'm reluctant to book in power runs for a specific time slot when I have cars booked on the rollers for mapping beforehand because sometimes the mapping session reveals unexpected problems that take time to sort out.

Having said all of that, if I had booked a car for a power run and couldn't get the car on for whatever reason then I'd have made sure that the customer knew this before setting off.

Comparing mapping and setting up to a dentists work isn't a level playing field IMHO.