> And now the tide is swinging back a bit as people get fed up with fakes and commingling at Amazon.
That isn't actually happening at all. That comes across as what you wish were occurring. Unless you're referring to eBay's share of online commerce persistently contracting as they stagnate. It isn't a new problem, eBay as a force in ecommerce has been eroding for many years now.
It's why eBay has a $22b market cap and their market platform has entirely stopped growing. Their stock multiple is so low because nobody believes in their growth story (it doesn't have one). Over four years they've seen an average of about 6% annual growth, although that includes other non-auction businesses they had acquired. It's also why they're a juicy takeover target: the lack of growth gives them a cheap valuation, combined with good margins and a difficult to remove quasi-monopoly position in auctions. There is no future for eBay other than in the belly of someone larger, and soon.
Amazon of course has been going gangbusters on growth during that time, becoming ever more dominant in online retail. The exact opposite of what you're describing.