Forged coins tends to sound different (gold and silver ring differently when dropped than cheaper metals), and they are different hardness/strength than cheaper

Forged coins tends to sound different (gold and silver ring differently when dropped than cheaper metals), and they are different hardness/strength than cheaper materials. If it's still gold/silver, but different design, it's just a foreign coin. They weigh it to figure out the worth. The tricky part is if the coin is clipped. Take a look at dime or quarter: notice the fancy edge? That was so if the edge got clipped, it's no longer fancy, and you can tell it was clipped and weighs less. This is actually an important property of silver and formerly silver coins: the different value coins change weight in direct proportion to value. So a quarter weighs 2.5x as much as a dime.