I think if you are selling tangible goods and your PayPal settings require a PayPal Confirmed address, that will require a credit card, since a Confirmed address would be a card billing address. Aside from that, I think buyers should not normally need to link a card to their PayPal account, so they can pay from their PayPal balance, bank transfer, or eCheck. Really, this is more of a question for PayPal support if you require further clarification.