Bottom of the page in the resolution centre
If you have a non payer you open a non payment dispute at the bottom of the page under Resolution Centre.
You can open one after 2 days and close after another 4 days.
You get your final value fees back the non payer gets a strike and neither of you can leave feedback.
If you dont do this then ebay do not know you did not get paid and you have to pay the fees.
You have 32 days to open a dispute
