How can China know you are not selling anything there is you don't report it? Or Russia, North Korea and the other 250 countries on this planet? You know your c

How can China know you are not selling anything there is you don't report it? Or Russia, North Korea and the other 250 countries on this planet? You know your computer is made in China and probably your clothes too, so you are doing business with China, do you report your income there?