I make a straight on turn, player has trips. River makes board straigh

[Spiffysean]

Well... Karma and the Poker Gods aside, he cannot say that he is playing the board.

Once he mucked his hand, the hand is dead, period. He could do anything else - Even if he tabled his hand and threw it in the muck, technically as long as he exposed his cards, in most casinos - the cards speak. Using that logic, I could fold pre-flop and go "crap, I would have made the nuts" and get part of the pot.

Personally, I would not give him his money back. You are well within your rights to keep it, the casino would support your choice, and let the nits at the table curse you for the good luck.

Think of it like a +EV thing. Much like a drunk donking off his stack to you, this is a gift at the table. He's a fish, and the Poker Gods smiled on you giving you an extra bit of money.

[ImThatGood]

Happened at my local casino, no i did not return money but did by drinks for him the rest of the night ($1 tip not full price) Seemed to make him happier