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