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If you logged into your account to pay for the item AND its within 180 days of paying then you should not have to provide that information.
If the seller goes into your transaction details on their account and hits the refund option then the refund would automatically go back to the funding source you used to pay in the first instance.
However if you did not log in to pay or its after 180 days then all they would need to refund you is your paypal email address, the one you log into your paypal account with and that identifies that account.
Advice is voluntary. Kudos / Solution appreciated.