Why do you care?
I'd say at least 90% (and probably more) of my Bonanza buyers are "new" to Bonz. Many have generic names, meaning they haven't even signed up for Bonz but are purchasing as guests through Google/
Amazon.
And as long as they pay for their items, use a payment method that gives me seller protection (and them buyer protection), I'm not sure I understand what difference it makes or why one would care about their Ebay ID.
May I ask why it matters to you? Do you want to make sure you aren't selling to a reseller and if so, who cares? IMO, you want to sell and they want to buy. That's the point. So what if they are going to flip it?
ETA: BTW, how does an ebay member have "110% positive feedback?"