Apart from shady gambling sportbooks that have ridge their system to prevent previous winners from winning on their site with probably exact strategy deployed the previous winning round, I don't see a reason why a previous winner shouldn't try his chances again of winning on the same site. Where it gets ugly is when you let greed lead you into over betting just to increase your chances of winning big. If you take some profit from your previous wins then rebet, there's nothing wrong I so doing and I'm ok with doing so.