Question Author
Understood hc. I suppose what I was comparing was Amazon's ability (and they DO of course handle money transactions between you and the sellers) to keep everything at arm's length, i.e. any queries, refunds, whatever, always go through Amazon. You never get ads or spam from those sellers (well not directly to your Amazon email, which again I keep as a separate account).
Paypal could institute something similar, thus closing one loophole where your Paypal account is exposed to public gaze. Haven't worked out the ins and outs, but they are typically uninterested in the notion, which as I say does worry some.
BillB