^The key is to simply find out if they are interested in the first place. As a fellow car guy, I find it pretty easy to strike up a conversation with anyone who has a car that I am interested in looking at/learning more about. I typically introduce myself with just my name, and then chat with them about their car. I usually inquire as to if they detail it or if they have someone else do it. Either way, I typically then continue to explain that I am a "detailing nerd" specializing in paint correction/restoration and ask if they mind if I check out their paint.
It is typically pretty easy to read whether or not someone might be interested in what you have to say. If they seem uninterested, thank them for their time - compliment them on their ride and continue looking around.
If they are interested, proceed to walk around their car and point out some noticeable defects in their paint. Make sure they understand what you mean when you say "swirls" or "haze" etc etc. Continue by explaining to them exactly what you do in order to restore the vehicle's appearance... starting with proper washing and drying, decontamination, polishing, and protection. They need to feel that you posses not only the ability to point out what is wrong with their car, but that you also have the knowledge and skill to fix it. Typically after this 10-15 minute brief walk around, I part ways by offering a business card and ask them to visit my website to see some examples of my work and then tell them I look forward to hearing from them.
Don't expect a call from every single person you talk to, but be sure that you have left an impression on every person. Even if they don't end up calling you, there is a chance they will tell someone else about 'that guy they met at the car meet who can fix your paint'.
-Zach
