Thanks for the tag @wellingnorth .
Your question just led me to find an interesting difference between US and UK on the buyer requirement settings page.
For the US if you click the little i in the circle for the payment method required before bidding option it says: "If selected, we’ll automatically process payments for auctions when possible."
And that is in line with what I've seen being the case for US sellers who select it - it is applied on some buyers but not others and it's not always clear why.
For example, last year one seller had their immediate payment required for offers setting overridden on a transaction and was told by support it was because the buyer was considered a "trusted buyer."
eBay also introduced "shop more ship together" as a test last year and recently announced it had been extended, allowing auction buyers to delay the payment for up to 7 days to allow time to find additional item from the seller and get combined shipping.
Interestingly, when I look at the buyer requirement settings when signed in on .co.uk, it doesn't have the same hedging language about applying the setting "when possible."
But that doesn't necessarily mean the same things don't apply in the UK - it's still entirely possible that eBay may simply decide not to honor/enforce those settings for some buyers for whatever reason and it could also be possible they might be expanding "shop more ship together" to the UK as well.
And I've also anecdotally heard from some sellers that it could be that the buyer was asked to provide a payment method up front and the initial authorization may have been successful, but then when the auction ends the final payment isn't able to go through for some reason - could be not enough funds, rejected for security reasons etc - so then the order sits in unpaid.
Sorry I don't have anything more definitive than that, but hope it helps!
