I think a compromise is that when a car is sold, the page is updated to mark that it is sold and a box shows that lists similar cars that match the initial car criteria.

What this does is not throw out the organic value of car inventory pages that have been index and instead of a broken link, provides guidance on similar cars.

What will eventually happen is google will mass deindex platforms that do not make the necessary changes.

I think indexed inventory is a very valid SEO solution if it is executed properly.

Great insightful post as always. Obviously if a car doesnt exist (isnt that the goal?) and someone searches for in, finds it in the SERPS, clicks and comes to a page not found, 404 error, or some other page that looks like a bait and switch then there will be issues. Proper use of a robots.txt file and xml sitemaps should help Google to find the real pages but Google is not always quick to the draw, and not many dealer web providers use sitemaps or handle 404′s properly.

One “best practice” that we use is to redirect any url to the homepage if any page is not found. It makes it virtually impossible to come up with a page not found. For example, try this page: http://www.mainlinehonda.com/paulrushinghotrodforsale

There is no such page, and you cannot blow up the web page. However, if a customer was really looking for a car, and it was indexed in Google, and the car was sold, at least we got them to the homepage and not some error page. It is the best alternative to avoid Google slapping us with a penalty which is perhaps why we have some high page ranks on some of our dealers websites.

With that being said, good argument against indexing inventory, but if it’s handled with better redirects or even better continued to list the page but marked the car SOLD, then that may be better.