I think you have to ask: why are people dealing drugs?
Some people sell drugs because they are desperate. These people are dealing with extreme poverty, trauma, mental and physical health issues, etc. Their cars are messy.
Other people sell drugs because of the economic opportunity. In my experience, these people pride themselves on cleanliness, timeliness, and customer service. They have clean cars.
When I started dealing drugs, I did it because my friends and I were smoking trash weed and we wanted to secure a good supply of quality product. It worked out well. My car was clean. I didn't sell much.
A few years later when I turned 23 I was diagnosed with rheumatoid arthritis. My life fell apart, I was bedridden, I went through a medical bankruptcy. That is when I began to deal drugs to survive. For a few years I paid my bills by selling weed, ecstasy, adderall, mushrooms, acid from the bed where I spent 95% of my time. My car was dirty.