Do you have any sort of portfolio online already? Anyone following you @petrol360 on IG yet? Anything posted?
Start with the research. Is there anyone else near you doing this? Anyone in the nation you can borrow a business model from?
Why do I want professional photos of a car I'm trying to get rid of?
If I'm a dealership, why do I want to pay you instead of making my sales manager take a few quick snaps with his iPhone and getting it online this afternoon, not next week?
Why do I hire you over the guy who also shot my wedding? Did my kids senior photos? That I see at the track who also races or who already shoots the track days and races I do?
What can you do that I can't with the DSLR I/my wife probably owns already?
You say 12 shoots a year... What are you going to do in winter to get the nice cars out? Or all 12 shoots in summer? How fast do you think you can do the processing turnaround?
What kind of lighting equipment (and experience with lighting) do you have? Any access to a large studio space? Cool locations scoped out? Access to assistants for larger shoots or video?