Another easy way to check for duplicate content is to grab a fairly large chunk of text from one of your pages and do a Google search with quotes around that chunk. In theory your website should rank number 1, but if it doesn’t and others appear above it – then there is a chance that these pages have “scraped” your content. If this is the case, it’s time to re-write.

This is also true – by duplicating content across several pages on your websites you are not providing the user with any additional / useful information. Small blocks of text that might be helpful on every single page, such as your contact details are fine but larger blocks can cause problems. If you think it would be useful to provide a Return Policy for example on every page it’s probably best to do this using a link that will open the Returns Policy in a new window. This means the Returns Policy page remains as a single page which isn’t duplicated and the other pages simply link to it.

I’ve talked a lot about the canonical meta tag in some of the responses below – the reason being that is probably the single most important tool that web master have to prevent duplicate content penalties, not only accross multiple domain names but also in a single site. Google release a blog post when the canonical meta tag was first release which explains how to use it.

http://googlewebmastercentral.blogspot.com.au/2009/02/specify-your-canonical.html

It explains how the tag can be useful for a site that may display the same content on several different URLs.

E.g. if you have a “Brand Overview” for all products of that same brand.

Or you have a “Return Policy” block of text for all products across the site.

Is this true?

This is a similar issue with the magazine style websites references above. The best way to achieve this is to place a canonical meta tag in the head content of the page with the duplicate content. The canonical meta tag references the original source of the content and Google recognises this.

Unfortunately this content that you have added to your websites is not going to give your site any SEO benefit because Google will give that benefit to the site referenced in the canonical meta tag. If you choose to omit the canonical meta tag then you will likely be penalised for duplicating the content.

I posted a link elsewhere in the comments to an SEOmoz article that references the use of the canonical tag.

Cheers.