Lynne,
As to credit cards over cell phones:
a) it's frequently hard to establish a solid
cell phone connection inside show venues. Last weekend alone, at both
the So.Attleboro MA show, and the Hampton Falls, NH Show..it was
impossible.
One because it's inside what used to be a civil defense shelter and we
all know we need to go outside to use our cell phones...the other
because there's hardly any cell phone towers around. And that's on
brand new fancy cell phones with Verizon service. (and on Sprint).

b) Even if that wasn't an issue..some collectors will understandably be
leery of handing a stranger their credit card. A stranger (the
'dealer') that they've never met before, who has set up at an
out-of-town show, and who may not be seen again. Not quite a problem at
regular local shows where 'everyone' knows 'everyone'...but certainly at
others.
That is a major advantage of PayPal, no actual credit card info. changes
hands.
Or of ATM machines l...

After all, at most shows, 'anyone' can call themselves a dealer and set
up...same way as they can and do on eBay.

Byrna