car classified project

We need a car classified site, which both users and agents can leave car classified advertises. The main purpose is basically this. The site should be able to cover traffic in rush hours and some search filters should be able to configurable from the admin panel. We can example [login to view URL] autotrader.com. The concept is like that and of course we have custom needs. I will give you more information after developpers sent me demo of what they did earlier. (We need developpers that coded already car classified web-sites since we dont have much time.) So our aim is to customize a done project for our demands. As for concepts I can give you [login to view URL] [login to view URL] and so on. We prefer ASP.NET and vb.net is better c# but not much problem even you have coded in php or not. All we need is a stable software. Thanks