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.