It's more believable if a gambler says he won big in slots and is still a winner because he never went back to play again. I know some people who did that.
I also believe that the only way to truly win at a casino is to permanently walk away once you’ve won an amount that satisfies you. Only then can the win be considered secured and fixed. If you return, there is a very high chance of losing everything or at least the most part of what you had previously won.