don't do it. I know with Scions when you go in for maintenance (like oil changes), they usually wash your cars. My relatives are all like "oh yea, that's how it should be!" but I beg to differ.
I'd rather not have my car sent through the swirl-o-matic. You can probably just ask the guy to not have your car washed. They usually don't mind, since that means that much less work for them. Just to make sure, I've heard of people putting (courteously-written) notes inside their windshields and other windows with instructions to not wash.