Could gambling be a good way to observe a person's nature?
For the current situation, I think there is not much that can be judged from someone's gambling activity that reflects the true nature of the gambler themselves. Especially if more people play online casinos that may not want many people to see their gambling activities. In the case of land-based casinos, I think it will also be difficult to judge someone's character. Except for the cunning and deceitful nature that is brought to gambling. Everyone has their own self-control. Some are good at hiding their true character in front of others. Some do show their true character, even with people they have just met.
We cannot know a person's character in online gambling because nobody is monitoring your mood or actions but some character traits can show in physical gambling. Some gamblers can be loud and complain a lot if they're not winning, you can tell that the person can be a complainer by nature. If a person is calm even while losing their money you can also conclude that they are gentle people by nature. But judging people by their temperament while gambling can be deceptive because they can choose to control themselves at the point of gambling, it might only be applicable when they're gambling. Composure in gambling doesn't mean that the person is gentle in other things, people can be calm it doesn't mean that they're good people.