When I say making a scene I am not talking about an all out affray or riot I am merely saying that the most successful way to complain in my experience is to assertively argue your point to the point where you exhaust the person dealing with your complaint and ultimately get what you want.
Ahh, the "Annie" Technique.
Annie was my Jack Russell that I had as a puppy. She loved to have a cup of tea in a saucer in the morning. If my Mum gave her the tea she would bark at it until it went cold and she could drink it. Annie thought barking at the tea made it go cold, when it was a fact that the tea would have gone cold anyway.
Lots of customers use this method to get their own way, when what they wanted would have happened with the passing of time anyway. Check in clerks have no authority to waiver charges nor do they calibrate the scales themselves. Its unfair to give them a hard time. Trading standards are your first port of call in this case.