Google’s John Mueller says to avoid copying the same structured data onto multiple pages of a website.
If a page needs to contain structured data at all, then it should be unique to that specific page.
This advice came during a Google Webmaster Central office-hours hangout where Mueller was asked the following question:
“Can a service review only ever be used on one page or can it be shared on multiple pages relating to the same branch? I ask this as we have reviews for particular branches and these are marked up. However, we also have sub-pages that are kind of general that we mark up too.”
Given that service reviews are marked up on a page using structured data, Mueller took a general approach when answering this question.
Rather than specifically addressing service reviews, Mueller recommended the following best practices for all structured data:
“So, in general, the structured data on a website, or on a page, should be specific to that particular page. It shouldn’t be something where you kind of say “Well, this is a review for our business in general, and therefore we’ll put it on all the pages of our website.”
Rather, it should be really specific to the primary topic of that page. So from that point of view I generally shy away from kind of mixing and matching reviews, and trying to put together a set of aggregated reviews that are based on what you’d like to have shown on a website. So it shouldn’t be, like, testimonials. It should actually be reviews.”
Mueller did not go out of his way to explain what would happen when duplicate structured data is detected on a site, but one can only assume it will be treated the same way as any other duplicate content.
With that said, when it comes to the body content of a page, it’s usually best to avoid duplicating anything regardless of whether it’s marked up with structured data.