If people cant satisfied with small amounts of profit and want more and more, for sure the end result will be very bad and we can refer to them as a bad gambler. Always put a limit for every gambling session is the best way to avoid such as bad thing to happen 'faster' in our gambling habit.
Bad gambler? seems like more of a greedy person to me. When someone wants to win more, it is normal however it doesnt really means that he is a bad gambler especially when he wins quite a good amount. Poker players actually live from gambling alone and that doesnt makes them bad when they just dont set their limit high
you can not live from gambling alone even if it is poker game and you are a professional poker player. or at least it wouldn't be a good life.
those professional players are doing so many other things on the side of their gambling to make money, from teaching others and getting paid to getting sponsor ads to make some money.