Forty years ago, a car insurance company sent me a refund check for $100. I thought maybe it was a reward for being a safe driver. So, I cashed the check, and spent it. Turned out they had another customer with the exact same name as mine, that the check was intended for. But they had mailed it to me, in error. Well, they tried for weeks to get me to return it. But I kept explaining to them that they had made it out to me, and the US Postal Service delivered it to my address (making it legally mine). Therefore, that was their tough luck. Eventually, they stopped calling me; and I never heard any more about it.