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I'm adding category pages for an online auction site and trying to determine if its worth marking up the products listed on the page. All of the individual product pages have product schema, but I have never seen them show up in rich snippets likely due to the absence of the price element and the unique nature of the items. Is there still value in adding the product schema even if the items won't show in rich snippets? Also, is it possible the product schema will help optimize for commerce related keywords such as [artist name] + for sale?