One important part of our solution here has to be that we force these companies to take a position one way or the other. So in Amazon's case it would need to decide - am I a platform for companies to set up there own online shop and provide fulfillment services to? Or am I myself the online shop?
In the later case they become responsible for product, like any business. In the former, they aren't. But in the former they now need to act as just a platform and not provide all the branding that makes it look like you're buying from Amazon. So they'd be more akin to Shopify or something I suppose. Every fly by night shop that wants to set up needs to set up its own branding and that way brand reliability and recognition still works and items are no longer commingled.