If you don't provide eBay with a payment method, they prevent you from making the offer
Today I was hit with the "default payment wall" when trying to make an offer. As noted by shermae, there was no way to proceed to the offer without accepting immediate payment upon acceptance of the offer by the seller. Later I asked the trusted and well known dealer if he did anything to set up that "default payment wall" and is answer was not knowingly.
HOWEVER I FOUND A WORK AROUND. As you got through the steps required, I selected PayPal and then within that selection, I needed to select which payment method (e.g. from which account handled in my PayPal wallet) and I chose one. The fine print stated I could update my selection in the eBay account settings.
Immediately after I submitted my offer, I went to the eBay account setting and deleted PayPal as the preferred/default payment method. There was not blocking of that action at all by the system. I did get messages that the new default payment method selection was made and a second one saying my payment methods were changed (after I stopped the default payment methods in the eBay account settings.
Doug accepted my offer so the item upon which I offered was not in the "pending offer section" nor did I see it in my eBay cart. That was not unexpected if the payment was made immediately and automatically by the eBay system. I even think I saw the item flagged as paid in the Purchase History" list.
So a few hours pass and I looked in my cart to see why the number displayed had increased by one. There it was, the item I make an offer upon and which Doug had accepted. It was awaiting payment. I went back into "Purchase History" and the item was now clearly showing as unpaid, awaiting payment. So I went back to the cart, and checked out by paying just this seller. The payment checkout operated as usual allowing me to first select PayPal then the account within my PayPal wallet.
Now I need to look up my PayPal login pass word, go to my PayPal account to check to see I was not double charged for the item, once automatically and once from my cart.
Hope this helps.