I'm not too sure I have understood your question, but is a buyer asking why they cannot choose to pay by a different method ? If you have accepted an offer the buyer has to provide a payment method and payment is immediate, it's a new ' feature' introduced by eBay. As a seller you can opt out if you wish.
Seller fees are charged the second an item sells, eBay allow a buyer 4 business working days to pay you, they also send the buyer a reminder after 48 hours to pay.
If there is still no payment cancel this Order selecting the reason .... Buyer Has Not Paid, they receive a strike on their account and your seller fees are refunded.
