This is a great idea! You are essentially guaranteeing our success by providing the demand search capability that users will build for you to promote to car dealers. Having the search traffic, it would be extremely beneficial for dealers to want to partner with you. You can go a bit further and provide with them the yelp model so they in return help you by pulling their own traffic to your app thus monetizing from both traditional ads and paid dealer memberships.
You can also simply offer white label services to dealers.

Great entrepreneurial spirit! Love it!
Humberto Valle #Unthink