Hi Guys, We have developed a plugin that allows us to display used vehicle listings from a centralized, third-party database. The functionality works similar to autotrader.com or cargurus.com, and there are two primary components: 1. Vehicle Listings Pages: this is the page where the user can use various filters to narrow the vehicle listings to find the vehicle they want.
2. Vehicle Details Pages: this is the page where the user actually views the details about said vehicle. It is served up via Ajax, in a dialog box on the Vehicle Listings Pages. Example functionality:  http://screencast.com/t/kArKm4tBo The Vehicle Listings pages (#1), we do want indexed and to rank. These pages have additional content besides the vehicle listings themselves, and those results are randomized or sliced/diced in different and unique ways. They're also updated twice per day. We do not want to index #2, the Vehicle Details pages, as these pages appear and disappear all of the time, based on dealer inventory, and don't have much value in the SERPs. Additionally, other sites such as autotrader.com, Yahoo Autos, and others draw from this same database, so we're worried about duplicate content. For instance, entering a snippet of dealer-provided content for one specific listing that Google indexed yielded 8,200+ results:  Example Google query. We did not originally think that Google would even be able to index these pages, as they are served up via Ajax. However, it seems we were wrong, as Google has already begun indexing them. Not only is duplicate content an issue, but these pages are not meant for visitors to navigate to directly! If a user were to navigate to the url directly, from the SERPs, they would see a page that isn't styled right. Now we have to determine the right solution to keep these pages out of the index:  robots.txt, noindex meta tags, or hash (#) internal links. Robots.txt Advantages: Super easy to implement Conserves crawl budget for large sites Ensures crawler doesn't get stuck. After all, if our website only has 500 pages that we really want indexed and ranked, and vehicle details pages constitute another 1,000,000,000 pages, it doesn't seem to make sense to make Googlebot crawl all of those pages. Robots.txt Disadvantages: Doesn't prevent pages from being indexed, as we've seen, probably because there are internal links to these pages. We could nofollow these internal links, thereby minimizing indexation, but this would lead to each 10-25 noindex internal links on each Vehicle Listings page (will Google think we're pagerank sculpting?) Noindex Advantages: Does prevent vehicle details pages from being indexed Allows ALL pages to be crawled (advantage?) Noindex Disadvantages: Difficult to implement (vehicle details pages are served using ajax, so they have no tag. Solution would have to involve X-Robots-Tag HTTP header and Apache, sending a noindex tag based on querystring variables, similar to this stackoverflow solution. This means the plugin functionality is no longer self-contained, and some hosts may not allow these types of Apache rewrites (as I understand it) Forces (or rather allows) Googlebot to crawl hundreds of thousands of noindex pages.  I say "force" because of the crawl budget required.  Crawler could get stuck/lost in so many pages, and my not like crawling a site with 1,000,000,000 pages, 99.9% of which are noindexed. Cannot be used in conjunction with robots.txt. After all, crawler never reads noindex meta tag if blocked by robots.txt Hash (#) URL Advantages: By using for links on Vehicle Listing pages to Vehicle Details pages (such as "Contact Seller" buttons), coupled with Javascript, crawler won't be able to follow/crawl these links.  Best of both worlds:  crawl budget isn't overtaxed by thousands of noindex pages, and internal links used to index robots.txt-disallowed pages are gone. Accomplishes same thing as "nofollowing" these links, but without looking like pagerank sculpting (?) Does not require complex Apache stuff Hash (#) URL Disdvantages: Is Google suspicious of sites with (some) internal links structured like this, since they can't crawl/follow them? Initially, we implemented robots.txt--the "sledgehammer solution." We figured that we'd have a happier crawler this way, as it wouldn't have to crawl zillions of partially duplicate vehicle details pages, and we wanted it to be like these pages didn't even exist. However, Google seems to be indexing many of these pages anyway, probably based on internal links pointing to them. We could nofollow the links pointing to these pages, but we don't want it to look like we're pagerank sculpting or something like that. If we implement noindex on these pages (and doing so is a difficult task itself), then we will be certain these pages aren't indexed. However, to do so we will have to remove the robots.txt disallowal, in order to let the crawler read the noindex tag on these pages. Intuitively, it doesn't make sense to me to make googlebot crawl zillions of vehicle details pages, all of which are noindexed, and it could easily get stuck/lost/etc. It seems like a waste of resources, and in some shadowy way bad for SEO. My developers are pushing for the third solution:  using the hash URLs. This works on all hosts and keeps all functionality in the plugin self-contained (unlike noindex), and conserves crawl budget while keeping vehicle details page out of the index (unlike robots.txt). But I don't want Google to slap us 6-12 months from now because it doesn't like links like these (). Any thoughts or advice you guys have would be hugely appreciated, as I've been going in circles, circles, circles on this for a couple of days now. Also, I can provide a test site URL if you'd like to see the functionality in action.