Q. How can some people be unethical in business even though they keep kosher homes?
What you eat and how you live your life are part of one and the same Torah. There are no marks for picking and choosing the commandments you keep, though of course it is better to keep something rather than nothing. But since keeping kosher is such a visible observance, it is not only God who must be puzzled to see kosher-keeping Jews being fussy about food and less concerned about honesty, but other people who say this is not a good advertisement for religion.
I have to add, though, that it works the other way too. It is to be deplored if kosher people are not ethical, but also if ethical people are not kosher. The Torah way of life is comprehensive; omitting ethics leaves Judaism lopsided, but so does omitting kashrut.