I only use the one P.O they know I always take a scan, years ago I was told I could not
take a picture of the letter while in the P.O. my answer was you have to be kidding.
Callan the quick way is not always the best way, if I was you I would go to the P.O and talk to the
person in charge, explain the problem, you cannot prove the weight of the bag because it show different on the receipt
but by bringing it to the attention of person in charge you might get a different outcome in the future.