I think on Folksy it’s just the paypal email address that’s important for payments - it obviously has to match your paypal account!
On paypal there is a box that has to be ticked to allow customers to choose the credit/debit card option if they want to pay by card instead of their paypal account. It’s in the seller options somewhere.
If you have postage costs set up in paypal ( e.g. for direct sales from your own website) then you need to override those for Folksy sales. That’s in the postage settings.
I don’t think there are any others. If everything looks ok, then a polite email to the buyer usually works for me, just asking whether they’re having problems at checkout, and that I’ll cancel the order after 24 hours if I don’t hear back. You can cancel the order at any time and the items will be returned to your shop if they don’t get back to you.