The entire sales process from searching & reviews to delivery. There are allegations that Amazon uses their data to identify the most profitable areas to set up their own competing brands and may even force sellers to disclose information which is helpful in this regard. If true, it seems pretty clear that a sensible antitrust rule would be to split those functions into separate businesses with strict rules about what non-public data they're allowed to exchange so the Amazon Basics guys don't have any information about what's selling where which you couldn't get.