I overpaid a guy 50 bucks once as a casino cashier, realised it as soon as he walked away. Security caught up with him and he gave it back no problem. He could have ended up banned but it was pretty clear by his reaction he didn't realise it either (most card players know exactly what their chips are worth, I paid out a 0.50 cent chip at 50.00$ ) It was the only time I ever screwed up....