Tom,
In the Cars.com approach dealers at least have the choice to look good/bad depending on how they work the system.
Not that I agree/disagree with having reviews linked to a 3rd party site, but it seems that the rest of the world has added reviews to their merchandise (Costco, amazon, Nike, etc).
One big difference is that all those sites have reviews about the product and not the business itself. You can't actually rate (that I know) Amazon or Costco. Last year I asked in a seminar that Yelp gave to car dealers if there was a lace to rate Yelp itself (since almost all the dealers in the audience hated them and the Yelp guy gave a 'no comment' answer to every important question) and they said that you can in their particular case, you need to look for them in SF.
There is a distinction between car dealers and Costco/Amazon even though they also provide a service as a business, but customers seem to be less forgiving to car dealers. As we all know here we only control some things in life and business. We are a dealer--Toyota makes the car--but it seems that when something goes wrong we somehow knew it. When a Costco purchased product goes wrong you don't blame Costco's employee.
I found this similar to the 'speeding ticket court mentality'. If you even have time go to the local court house and seat to watch the traffic court cases. Almost 80% (you will be amazed that it is probably higher than that) of the people that go complain about a ticket talk about 'how mean the office was', or 'disrespectful, etc. People say that hoping that the judge will do something about it. Sometimes the judges are even meaner than the cops... sometimes they just don't say anything other than "pay the cashier on your way out"... sometimes they explain that if the cop was 'insulting' or 'disrespectful' that they can go to the police department and file a claim or complain, but right now what is a stake is the fact that you were speeding. The officers mood is not relevant to that.
I equate this somewhat 'entitlement' that a lot of people expect from the police to what they expect from the dealers and that is why I don't see a clear way for dealers to manage this (the most absurd and insignificant turn during the process turns into a negative review). That is why I agree that 3rd party sites should stick to what they do:
Showcase the inventory I pay you to carry.