I am a little unclear what you mean by an advertising revenue model. There are two ways to implement this model: 1. Have dealers pay you to advertise their inventory on your site - similar to AutoTrader and traditional classified sites.
2. Run AdWords or some other advertisements on the site to earn money.
We had a true reverse auction platform where customers selected 3 identical/similar new/used vehicles and we initially pushed for a charge per car sold model (ie TrueCar). But many dealers had been turned off by TrueCar bad reputation and it's struggles with charging a similar brokering fee, so they weren't interested in AutoRef's service at all.
After that we went for a flat monthly fee but ultimately it was too little too late. So it's possible that your idea could work but we sure had a tough time implementing it.
TrueCar has always had a consistent revenue stream from its acquisition of Zag - which ran the car buying program for many car insurance company's, AAA, etc. This is a definite edge over a startup bootstrapping ad revenue.
Story about AutoRef: http://techcrunch.com/2013/04/11/like-a-carwoo-for-used-cars...
Car dealers seem to exhibit cartel-like behavior in various ways, so it seems like it will be difficult to drive real participation in a marketplace like this without proprietary demand (ie buyers at large scale that dealers wouldn't otherwise have access to).
The used car market might make a better entry point, because it's actually difficult to fully market a used car as a consumer, and aggregators like Carmax are known bottom-feeders, and their bid-ask spread is too high for the value they provide.
Another approach might be to do a hybrid involving car brokers or a merchant model, something more like what Zillow and Stubhub do.
If you do this, please invite me to your beta!
CarWoo attempted to create a better system. They actually came close, but ultimately failed.
It's easier said than done. One of the most difficult parts is to get dealers to participate.
I think a reverse-auction situation could work very well on a small scale. Maybe you could make a simple app/system for running your own reverse-auction effectively/simply? Keep it relatively small so dealers don't put up a boycott or similar.
Not sure this is the correct format for any of those options.