Proof that you're given satisfaction (7)
I believe the answer is:
receipt
'proof' is the definition.
(I have seen 'Proof of purchase' mean 'receipt' so perhaps 'proof' could also mean 'receipt')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for receipt that I've seen before include "Formally acknowledge" , "old-fashioned instructions for cook" , "voucher" , "given for payment" , "Sales slip" .)
