Duplicate content is not an issue any more
What is duplicate content?
Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar. Most of the time when we see this, it's unintentional or at least not malicious in origin: forums that generate both regular and -down mobile-targeted pages, store items shown (and -- worse yet -- linked) via multiple distinct URLs, and so on. In some cases, content is duplicated across domains in an attempt to manipulate search engine rankings or garner more traffic via popular or long-tail queries.
Duplicate content is not an issue any more !
According to Google, duplicate content on a site is "not grounds for action (penalties) on that site unless it appears that the intent of the duplicate content is to be deceptive and manipulate search engine results." That’s a very clear statement. Since most SEOs are of the white hat variety, Google has made their position on duplicate content clear and outlined some best practices to clear up any issues.
Non-malicious duplication is quite common as many CMSs don't handle URL construction and organization very well by default. When Google duplicate content, it is because variations appear in URL parameters (as provided in the example above.) When duplicate content happens, the URLs in question are grouped into a "cluster." From there, Google selects the one URL that best represents the cluster from that group, and then consolidates properties of the URLs in cluster (such as link popularity) to the representative URL.
If you do spot a case that's particularly frustrating, you are welcome to file a DMCA request to claim ownership of the content and let google deal with it.
Use sitemaps. If you want to tell Google which URL should appear in the SERPs, simply make the necessary modifications by including that preferred URL in your general sitemap. Should Google be unable to consolidate all of the duplicate pages, page strength might be diluted and your ranking may sink.[vuheart]