SEO - many similar product pages

[Fabelo]

Hi fellows,

We currently operate a marketplace on Shopify, using a shopify store app which enables various vendors to sell on our platform to end consumers (like any standard marketplace). We are trying to find a solution for SEO to the following: 

1. We want to use the collection page as a product page, : reason is that for one single product (e.g. iphone 12, we can have a few variants (storage, color) and many vendors. However we just want to show the cheapest price for each product option. So iPhone 12 Red 64GB will be sold vendor A, but maybe the iPhone 12 Black 64GB will be cheaper at Vendor B. Hence we will fake a proper product page, and instead create it at the collection level. Behind each "fake variant" of that product page (e.g. collection page) we create, there will be a product page. --> this page will be SEO optimized and is the one we want to push
2. However we will have many product pages for each collection page which will  not be SEO optimized (and all more or less the same content = many vendors selling the same phone will haver a 99% similar page in terms of content)

=> We are thinking about non-indexing all the product pages in future and focus optimizing only the collection pages (1.). In general, I think it's in line with best practices to focus on fewer relevant than many low-value pages, correct? But does that also apply to situations where a large number of pages will be noindexed, or will this affected the whole website and the remaining indexed pages negatively?
Thanks for your help!

[KieranR]

So I'm just gonna have to lay out some thoughts because there is a lot going on here. 

• IMO Shopify is not the best platform for a "marketplace" type site, the backend and frontend are just not built to support it in many ways. There are a couple of OTS marketplace platforms like Sharetribe or Nearme that seem a lot more robust when I've looked into this before.
• For (1) this should be doable afaik, with some decent custom coding, not sure if there are some product properties that are inaccessible on a collection page. 
• For (2) you could also look at canonicalizing to the "best" or "cheapest" in your case PDP
• If existing pages are getting lots of traffic and you noindex them, that's probably not good. Usually a redirect or canonicalize is better to transfer any link equity over essentially saying "this other page URL is the one to rank please, Google"
• The only issue I foresee is if you have a lot (like 10s to 100s of thousands) of PDPs that get linked to internally or via sitemap, that you could end up churning through your crawl budget and might have an issue getting all your pages discovered/crawled/indexed, or getting them crawled often enough. How big of an issue would depend on how many pages really.
• Setting up product feeds and JSON-LD schema will have to be pretty custom, and any review stars app is probably going to not work right at all. 
• There will probably be other side-effects/risks of this whole structure that are harder to anticipate.

[Fabelo]

thanks a lot Kieran for this - will explore a bit more the redirects / canonical options !