Do you ever go to a drug store and see a table set up with some stale cookies and coffee? Notice that they are always selling a service for people who frequent these places the most like Diabetics, elderly, athsmatics etc.? Why not do the same for auto detailing?
Go to a large real estate office and ask if you can "sponsor" their coffee and refreshments for a day. Buy a large box of
quality donuts. Just be sure these are the best donuts available (on par with Krispy Kreme) because you want to show potential clients you will not skimp on anything. Get a large keg of quality coffee as well as some juice. Add some cookies, bagels, fresh fruit or whatever people like in your area prefer and arrange them neatly on a table with a neat classy table cloth and napkins.
Get a local print shop to print a folding card that says something like "Refreshments courtesy of Santini Automobile Detailing". I would have the table arrangement and card look like something you would expect to see at a wedding or funeral.

If everything works out right, you will have a captive audience for as long as it takes the person in front of them to get their refreshments and return to their work area. If there are 50 well paid real estate agents, mortgage consultants, lenders etc. in the office that day, you can expect that every one of them will stop at that table at least two or more times in the day.
You should have your fliers with business cards inside arranged neatly on the table. It would also be a good idea to have some before and after pictures of high end vehicles you have done in a few small photo albums or scrapbooks. Be sure to thoroughly clean the area at the end of the day and ask if you can leave some business cards and fliers behind.
You could provide this refreshment table for less than the cost of a complete detail and at the same time reach out to potential customers, most of them owning high end vehicles that are part of their image. Even if you get one job out of it you will more than break even. If you get two or three regular customers, you will surely make your money back several times over in the short term. Just be sure to pay attention to every detail. They will notice.