Goldsmith cheating in grammage
OP, DarThere is a specific Act- the Weights and Measures Act that protects you. Infact such scales are to be regularly inspected and you have all the rights to report this to the Weights and Measures Agency (WMA) who will take appropriate action. The WMA can both fine and imprison such a sonara.
You also have the right to report this to the police for investigation as this is a cause of concern for all purchasers of gold from such sonaras. Such behavior amounts to a criminal offence which is imprisonable.