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I agree with Laura, Big Commerce, OpenCart, OSCommerce, these would all be great solutions. I think Big Commerce is the best hosted platform on the market right now. OpenCart and OSCommerce are not hosted solutions, and they are both open source so you would have to have some coding experience to get them set up.

They are mostly permanently out of stock /  out of collection. Based on research and your reactions we want to 301 redirect them to the relevant category page. The number of 404 errors in webmaster tools are quite substancial. The ones which are not permanently out of stock but temporarily unavailable we want to maintain the product page with a comment that the product will be orderable soon.

Try the Google Ad Preview Tool: https://www.googleadpreview.com/ Basically, with the Google Ad Preview Tool you can view the Google search results for Google AdWords (Google Shopping & Paid Search) and Google organic search results based on the location (Country & City), Devices (Desktop, Mobile, and Tablet), Languages etc.