Here is a real auto sales site that has boosted his sales 20%. You can put a featured vehicle on the main page or just switch out a different picture from the backend,

This is the manager backend that drives the used vehicle listings, as well has a simple system to store contacts and offers for the site above.
You can easily add a vehicle listing, change it, delete it or just set it to not show.You can also store sales leads and contact them via phone or email. Of course on your site, these backend pages, the whole /manager directory, would be protected by a username-password prompt

Of course, you can't alter data data or delete pictures, to avoid e-vandalism. Of course, as the owner, you can alter it yourself.