ojread2, we don't know op used a mobile number, only that their seller did. Doesn't have to be a landline number, on eBay or Paypal - mine isn't, starting 070. And I see no call for the seller to ring a buyer "straight away" regardless of fb or price, not before they've given a buyer a chance to pay ! If they were concerned about fb, the seller should adjust the auction accordingly, preventing bidders with low fb bidding.
Think I only ever rang a winning bidder once, after quite a few e-mails were ignored, and a couple of weeks later. That was a high value item I was selling for someone else, and turned out the winning bidder was a minor, I spoke to their father who was mortified (but did pay !).