I am wondering if she is looking at the right side of an item rather than on the right of the whole transaction at the top.

It can make a difference and a common mistake.

 

But if you have already progressed with a new listing, keep going with that.

In future if the buyer uses the cart, it enables the seller to combine the postage costs providing the listings are set up correctly.

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Not having seen how she tried to unmark as paid, I'm not sure where she tried. As of now, I have suggested she do the cancellations and we'll proceed from there, but I will probably have to wait till tomorrow for that (as it is now midnight).

It became impossible to send a revised invoice once checkout was completed with bank deposit selected several months ago, unfortunately, so cancelling is the only thing you can do to ensure eBay don't charge the fees on the higher postage cost.

She has agreed to cancellations, which I have now done, and then will make a special listing for her.


@davewil1964 wrote:

If immediate payment is selected, the only payment option is Paypal.


That's true when the seller selects immediate payment.  If ebay opts you in without your agreement you can still offer bank deposit, as I do.  If the buyer doesn't want to pay straight away all they need to do is select bank deposit when they go through checkout.  From what I've seen in these forums lately, a few non-payers seem to be deliberately choosing bank deposit and then never paying, which is why I'm considering removing the bank deposit option.