It’s fair to say that there’s been too much written about ‘duplicate content’ over the years, making many website owners more worried than they should be about it. Doing the obvious technical things to present your websites unambiguously to search engines is sensible. But it’s unlikely that many companies will find themselves ‘penalised’ by duplicate content.
Indeed, there is actually no ‘penalty’ as such – it’s just that the search engines try to present just one result for any particular block of text, and if your page is not the chosen one, you won’t get that result. So, for example, if you distribute a product for a manufacturer, and your text about that product is just lifted from the manufacturer’s site, it’s quite possible that your page won’t appear in the search engine results at all. If you have the same copy on multiple pages, will it be the one you’d want which gets shown? If you have the same page multiple times, could any external links be distributed amongst them, diluting the impact of the links?
Where some sites think they’ve been penalised is usually because there’s so much unoriginal text on their sites that hardly any of their pages are showing in the search engine results. This can be a small issue for some businesses, but it’s a major one for websites which do nothing more than reproduce other people’s material. An example of this is the type of magazine site which does nothing other than publish press releases. If you think that sites like that seem to send you very little traffic, it’s probably because they have very little presence in the search engines nowadays …and consequently, very few visitors.
There are a few tools for checking your site for duplicate content, although I like to grab random sentences from the middle of product pages and paste them into Google to see what comes up. Not only should you be describing products in different terms to other sites (such as manufacturers and distributors), but you should be aiming to do things better.