#3: Denial/Concealment: Most addicts are in denial. They would never admit to having a problem. However they probably subconsciously feel that something is wrong or at least there is something they should not be doing. If you are hiding your gambling habits from friends or families, you might already know deep down that there is an addiction already.
It seems to me that this is the most obvious indicator of a problem gambler, because they often start lying and not showing this hobby to their wife, girlfriend, or family. And the thing is that they behave so secretly because they understand that their family will probably not approve of such a hobby. And they are right.
We all know how society treats gamblers. Of course, a gambler can lie about winning and getting winnings from a casino, but I think that his inner state will give away the gambler's true mood. If he actually loses, he will always be angry, even more secretive. But sooner or later, any gambler loses.