when the item sold Amazon charge me fees 82.47 and when I did the full refund they refund buyer only 77.47 and they charger me the different $5 .. My question why would they keep $5 from the fees and charge it on me ?
You may think so but Amazon did incur costs processing the credit card payment and then the refund. As a result, Amazon keeps up to $5 in an ‘Administration Fee’. If you refunded partially, they still would have kept a partial amount in an ‘Administration Fee’.
This is how it is supposed to work, whether you agree or not. You can read about these fees from the following help page:
Refund Credits and Administration Fees