Though I'm not (and don't want to be) a detailer I do have similar experience. I was a freelance graphic artist, and now run a family owned law enforcement uniform/gear store.
Detailing is much like design: you are selling your experience and your time. That's probably why the CL ads with before and after shots were so successful. But in design, as in my store or any retail style operation, you are going to run into people who want the most for the least they can pay.
As others have suggested maybe you can offer an intro to detailing pack. I can't say what it would cover, perhaps a wash and wax and some light interior cleaning. I would definitely make it clear in any ads that the work shown required extra work. But the pack could work as a sort of "car wash plus" for people who want more than a machine wash but less than a full detail.
Just a suggestion.