Hi,
It is actually important to let the search engines follow the links to your products if you want a good SEO. So I would recommend to enter a canonical URL for your products and that will avoid the duplicate content SEO errors.
Nevertheless, if you want to add a no index rel to your categories or products links, you need to edit the files listing_img_title (or the view layout corresponding to your item box layout options) of the views "categories/products via the menu Display->Views and change the a html tag of the links to include that no index rel attribute.