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

Per my knowledge the middle east & Saudi Arabia offers a great market for user cars. People are passionate about driving the latest & trendy cars.

From your description above, you have access to a captive & engaged audience that you can market this platform to. Used card Online dealerships are also picking up in North America. Checkout platforms such as www.beepi.com & www.truecar.com. They have been able to prove the online model and also successfully raise funding.

Key ingredients for their success is they don't just serve as a portal for used cards such as auto trader, cars.com etc, instead they get involved in the buying & exchange of the used cars themselves. Thus ensuring they provide a great user experience for the buyers & sellers, at the same time there is opportunity to make money during the entire process.

With used cars being regularly sold & exchanged in Saudi Arabia, this seems like a strong opportunity. You could see better success by looking at the opportunity to solve the problem end to end instead of just serving as a lead-generation website.

I have complete experience in launching marketplaces similar to this. Happy to engage further.

good luck!