I detail out of the trunk of my Lexus
Interestingly enough I have never had anyone mention anything to me or even give it a second look until the other day when I did a Cabrio and the woman thought it was funny. She said "Interesting work vehicle, I was expecting a van or something" I replied "When you do good work..." she laughed and went inside. That was it.
I think it really depends. Around here you have a lot of self made people that understand the entrepenurial spirit and they even seek out the smaller lower volume people, like us and the trunks of our personal cars, because they understand that you tend to get a better job out of a professional who owns their own business than some guy who gets paid hourly driving one of 50 trucks. One customer told me that he loves the "Underground Economy" and hardly ever does business with big companies.