In real life, I just smile and people do understand that I do not want to answer the question - at least by the second time. I wonder if that would work on WeChat too.

For a phrase to tell someone that I dont want to say something, I would use a construction with 我不太方便....

It clearly says you wont say something, but to me it feels warmer and not as direct as \"I cant/wont say\"

You don\'t have to be the polite Canadian (American, whatever) and answer or even feign answering every question. Deal with questions you feel comfortable dealing with and just ignore the others. No matter how many times how many ways your supplier asks again.

\"Just politely tell him that you are unable to divulge such information.\"

f we were negotiating in person, I would chuckle and shake my head. Maybe wag my finger too. (Try to make light of it; not flare up in anger.) It\'s not up to you to invent some subtle dodge. If all else fails, just say \"I don\'t want to tell you that.\"

It\'s completely normal behavior for a Chinese business colleague or counterpart to disregard what you see as your boundaries and ask such probing questions.