Moral Question?

I was paid 2 to 1 for a blackjack and pointed out to the dealer that he overpaid me. The other people looked at me like I was crazy for giving money back to the casino when the dealer made a mistake. I told them I wanted to win fair and square. How do you guys feel? Do you just keep the money or do you give it back? I'm just curious. When I first started gambling in casinos I would always keep the money if I was overpaid. I asked my dad about it and he said he always gives it back so I do too. What do you do?