Well, banks are not stupid, and it is cheap for them to certify gold bars in quantity.
There are certification authorities that do exactly that. Here in Spain you can hire them, and they will melt the gold in front of you and use expensive instrumental to know how much gold a gold bar has.
We also have the concept of "notary" that is a person whose job is to certify something by law. They are trustworthy.
It is individuals who should be afraid of being tricked. But you have at your disposal cheap microbalances, micro ohm meters(I made myself one for like USD30), 3d scanners(to calculate the volume as using water is tricky because surface tension of water), quartz transducers to measure speed of sound.
There are certification authorities that do exactly that. Here in Spain you can hire them, and they will melt the gold in front of you and use expensive instrumental to know how much gold a gold bar has.
We also have the concept of "notary" that is a person whose job is to certify something by law. They are trustworthy.
It is individuals who should be afraid of being tricked. But you have at your disposal cheap microbalances, micro ohm meters(I made myself one for like USD30), 3d scanners(to calculate the volume as using water is tricky because surface tension of water), quartz transducers to measure speed of sound.