Recently I was around a physical bet shop close to my area and I observed a man who was shabbily dressed walking in the gambling house. I got into the place to observe what his intentions were. He walked straight to the gaming attendant, placed his bets in a highly coordinated manner and quietly walked out of the physical gambling house. From the way he was well organized, you will never know that he was mentally unsound apart from his dirty clothes and unkept hair and beard.
When I inquired from the attendant, she said he was a regular customer and that he usually raised money for gambling through the manual jobs he does around the area. She also told me that he has never misbehaved and acted violently in the gambling house so she was comfortable with him.
My question now is are there any moral, ethical or legal obligation to bar a person from gambling after physically observing that he is mentally unstable?
What a weird way for you to describe judging someone based on their looks. For you he may have looked "shabby" but he might otherwise have been perfectly sound of mind and you say that he was otherwise organized enough to place a bet. Some people do not choose to conform to society or the way that you think they should look. Nothing else besides his appearance in your description makes him seem mentally unsound. It's also not the cashiers job to reject someones business really and it might create genuine barriers for people who otherwise should be allowed to gamble. Do we stop people gambling when drunk? As that would suggest they are making improper decisions? No, we don't - in fact casinos often try to ply gamblers with free drinks in order to loosen them up a bit