I do not believe in anything called professional gamblers. I see it has something that can be deceiving because there are rich people that can go broke at anything. Gambling can be one of the reasons if you solely depend on it.
It is just a label since it is mostly a personal occupation.. Professional gamblers are people who are regulars at competitions, or have their income primarily from gambling activities like poker. In some countries, participants in certain gambling competitions need to register for tax purposes.
Even on the gambling site terms of service, it is highly advised that people should gamble just for fun.
True that but we cannot remove the fact that some people get more serious about their gambling activity, either for profit taking or bragging rights.