If you're a gambler, then control and manage how you're gambling before it get worse to the extreme stage, also, if you're privileged to see someone gambling in the wrong direction, take it a responsibility to call them into order, some things were better done or dealt with in the early stage before they got worsened, having desires for gambling is not getting yourself harmed by gambling because if ignorance or lack of self control while gambling, the gambling platforms will not control you, it's your own responsibility to do so for yourself.
It is very rare that people listen to others when it comes to this as they will feel judged, and they will think that you are overstepping their boundaries by doing something like this, so even if you were correct on your observations about their gambling habits, you can bet they will continue to gamble as usual, and even if at some point they realize they had a problem you can be sure they will not remember that you tried to help them before things got out of control.
It is very difficult to advise someone who is addicted to playing gambling, because many of their friends or family will ignore them so they don't continue playing gambling, even though they use various methods, that person still continues to do it, the only one The way to do this is to wait for the person to experience financial difficulties in order to give a deterrent effect, but there will be something crazy that he will do in the future, even though it will be a big problem for himself, it is better to let him get into a big problem than to waste his words trying to advise him.
That's a really weird way to go about someone who is gambling and has addiction problem. No doubt that advice is like a total waste of time but I still prefer other method than allowing the person to gamble away and get stuck because in the process like you said he might do some dangerous and unthinkable things just to achieve his addiction urge and you allowing him to do so is really not the best way to go about it.