A rich man will never say how much money he has.
But you can notice it based on how he handle his/her money by spending it. They pay taxes and it's impossible for them to not know their assets. Even the government can investigate on how much money you have. A rich man is silent but he is obviously proud of what he had. It is the fruit of his hard work and it is normal for you to say that you are rich enough around the world.
I completely agree with you that its very difficult to hide wealth from a person. In most cases, a person who has long been rich, and especially if he suddenly became rich, develops a very nasty character trait in which he cannot restrain himself from the various habits of rich people. Such people very often do not behave modestly and scatter money from left to right. If a person begins to spend more than he earns or more than declared, then public servants will definitely have questions of a certain nature. I believe that living modestly, while possessing great wealth, is very difficult.