Agree with Kenneth that this is a crowded place. My suggestion would be to niche it down and focus on the supplier side accordingly. It could be based on:
- type of supplier (rental car agencies, seniors, married people looking to give-up their "fun" car for a kid-friendly car, etc.)
- type of car (could be brand, model, year, and/or category specific)
- serving geography (could be from a specific set of locations)
- and more

Hope this helps!