There was a case like this in the local newspaper recently. An older woman cashed 6 $20 gold coins. The teller gave up $120 cash out of his pocket and pocketed the coins. He was subsequently fired and the bank (IIRC a Chase branch) manager noted that their tellers are supposed to inform patrons of the true value of their coins before accepting them.

Hmm I'm involved with a FIRST robotics team at a local high school and I've seen rivets used on some quite advanced machines recently. I've even seen what happens when a persons hand ends up where the pieces of metal to be joined are supposed to be. Lets just say that I'll be quite careful not to repeat that mans mistake.