Penguin goes after over-optimization, and spam both on-site, and off-site:
Google Launches "Penguin Update" Targeting Webspam In Search Results
The two things I would do are:
1. Make sure that you are using keywords in your links less than 10% of the time, digging down to page level metrics, and disavowing any spammy looking links.
I have a dealer who had a bunch of links from pages that were just pure links, and no content. So, I attempted to email the domain owner, which of course failed, and then just disavowed it in webmaster tools. I also make sure that we are link building towards branded, and benign links so that we never get over-optimized, leaving us in the grasp of a Penguin updated, or too spammy, which would put you in the range of an unnatural link penalty.
2. Making sure your content is pretty much grammatically correct, and not keyword stuffed.
If your content reads like this, then you might want to rewrite it:
The best thing about having a Dodge Dart in Minneapolis, is that you will be one of the first people with a Dodge Dart in Minneapolis and be the envy of all the people that want a Dodge Dart in Minneapolis.
Also watch out for things like this:
Our dealership is a great Buick dealer MA. As a MA Buick dealer, we pride ourselves on fantastic service.
Forcing in keywords with bad grammar continues to be less helpful for SEO, and even worse for conversions.