Car Valeting - Drying the upholstery

In the past when I've had my car valeted, (By the same crowd,) they've used some sort of convection heater and dehumidifier after shampooing carpets & upholstery.

Recently I left the motor into one of those crowds that operate in shopping center car parks, was told two hours so off I popped.
Came back 2.5 hrs later, the car was idling, all windows down and the climate control at full blast. The LCD backlight on the heat control had gone, (I can't see what degree it's set too.)

When I asked, first he said that it could have already been gone. I assured him it certainly was not. He then said maybe that the heating had been full blast on for 2 hours while the car idled which may have caused it to die,

I can replace the display easily enough. But surely leaving a car idle and heating at full tilt can't be good for the engine or standard valeting practice? (2004 Alfa 1.8 Petrol)

I've to go back & speak to the bossman tomorrow, do I have legitimate comeback here?