Welcome to the Q&A Forum

Buy a magento car theme at template monster. Or buy one on Magento Connect. On magento connect, you will have to do a lot of digging around. The themes are already set so you just have to get familiar with it and change the pics

There isn't really anything you can do to impact this.  This is not a good strategy for your competitor, and I'm not even sure how much it could potentially be benefiting them.  Google will realize the duplicate content and then serve the page that has a higher authority as the result that actually matters.  If I do a search for bozeman chevroletand montana chevy I actually see the Montana Chevy website coming up for it's root domain search, but even when I search the exact match Bozeman Chevrolet it doesn't even come up on the first page.  This tells me that Google has established the origin of the content and higher authority domain as the Montana Chevy website.  In reality that may be true or false, but that's what Google has decided.  If you run OSE reports on both domains you'll see why Google has decided the Montana Chevy is of higher importance because of all the links that point to it. I would just let your competitor go about doing this, because I don't believe it actually gives them any real benefit.

Agree with EGOL on the complexity of this issue.  Seeping decisions on this can be dangerous.  One point I will speak to is the duplicate content on the search results issue.  I assume you are running into this problem because your search results pages are being indexed by google, and many of them show similar content.  There is no consensus on this issue right now, even from Google.  They will not penalize, however, because of duplicated content found in search results.  So i wouldnt worry about that problem right now. As for the expired/sold inventory pages, i would say to either redirect to a more permanent page (like a ford explorer sub category page for all explorers) or you just delete those pages, making sure that you manage your sitemaps and urls on a regular basis.  But that usually takes too much time.