The violation of ethics for money is an age old story. A man hires a hit man to kill his wealthy wife. We've seen countless real life stories too. Headlines like this one about the woman who poisoned her husband for money. However, you don't have to be a criminal to compromise your ethics in the name of money.
Some ethics violations are more socially acceptable than others.
Take the issue of other people's money. I'd give the money back to the person who gave me too much change. You are an angel. I know, can't you see my halo. I'd keep it.