Ummmmmmm, you run the customer's car for 30+ min ? Idling ? There's a couple issues with this...
- Many municipalities have anti-idle bylaws. Even if yours does, what are the chances of getting caught ? Probably miniscule, but none the less, it would be illegal.
- What happens when the customer notices that their fuel level is lower (depending how cold it is outside, or how "untuned" their engine is, it could be a significant amount of gas spent) when they pick up their vehicle ?
- What happens to the excess carbon you build up as a result of letting it idle for 30+ min ?
- Some folks, like me, are very particular with time / usage sensitive maintenance, such as oil changes. Idling the vehicle 30+ min expends oil life, so how do you communicate to the customer that they now need an oil change in 1500 miles instead of 1700 miles ?
- Many people are environmentally conscious these days, how do you explain to them the amount of CO2 gases you just released to dry their interior ?
Sorry if I come off sounding like an ***, but I would be supremely mad if a detail shop idled my car for 30+ min just to dry the interior. As a professional in the industry, I would do this only as a VERY last resort, and I would make sure to let the customer know that it was done and why, and I would also discount the final invoice to account for fuel spent.