I think the way to spot a gambler addicted is they are trying to borrow your money to gambling. That surely is a gambler addicted.
That is 1 trait of a gambling addict also the lack of activeness of a person to communicate with other people and just focus on gambling alone, been thinking hard on how he/she could win the losses on a game, always blabbering about gambling non stop.
Yep, these are some traits but i will also like to add that people that don't seem to have anywhere to go apart from the gambling house and spend all their time of the day over there are addicts and they might be seeking to make recoveries at such times that's why all their lives are spent over there thinking about strategies.
Wasting too much time just thinking about strategies about gambling all day long without the regards of oneself, there are even some gamblers who even forgot to eat thinking about this and that to win a game which makes them more prone to losing in gambling.
Regardless if he is a gambler or not, I think we should not waste our time spotting if someone is a gambling addict or not. Though one exception may be if the gambling addict is your friend, family relative or someone close to you. I know that there is this initiative of helping a stranger to control his/her addiction but the changing of habits purely depends on their decision as an individual. Even if we exert some effort to help them, most of them would just return to their original ways. I know that even though are efforts are for the needy, some people are just close-minded when it comes to these things. The only way to help them is for them to help themselves.