Most review sites, for example sites that review games with different platforms, will often have three URL's with identical content, only differing in color schemes, and of course comments. This is true of some large sites like ign.com.How do these sites deal with duplicate content? Do they use a rel=canonical link to point to only one URL?
What do large review sites do when duplicate content is unavoidable?
seo;duplicate content;canonical url
Yes, this is what they should use to indicate where the original content can be found, especially if they want that content to be indexed only for the main site/page that it can be found on.In the case of ign.com, I can see they have in their HTML source code:<link rel=canonical href=http://www.ign.com/ />Without knowing the other URL's that you're referring to, I can only guess that they have this link in them also whenever duplicate content can be found. The alternative would be to specify in robots.txt not to crawl these other review pages.On the other hand, if they want the comments to also be indexed, and they are not dynamically generated or too complex for the search engine bots to index, they might just leave it to the search engine bot to decide. In this case, they would have pages competing against each other for the same content, with the potential of the main site/page losing out.Here's a link from a Google Webmaster Tools answer for more information on this: About rel=canonical