Re: If someone mistakenly sent you 1 ETH, what would you do?
Receiving ETH, BTC or any other altcoin by a mistake is pretty impossible because there are so many possible crypto addresses (billions of billions?). So he has to know your address and then send it to your wallet for example by copying wrong target address. And what I would do with it? Nothing, only if he contacts me for example by sending me a token with the name "Sendback" for example, I will return. 
But you never know why you receive the transaction and what his intentions are. 
Right, I rather worry if someone got a hold on my ETH address and sent me 1 ETH out of random. You would never know how easily you could fall into someone's trail of "dirty ETH" if you sent it back. Me? I wouldn't send back 1 ETH unless I'm sure not falling into anyone's pawn. But you never know why you receive the transaction and what his intentions are.