Negia

Question

I read your response to questions of negiah- my question is if someone extends a hand to me and it's in a business setting- do I have to refuse to shake her hand? Second, if someone elderly asks me to help her cross the street, may I and if so- how is this also not a breech of negiah. As well, if my family is not religious and taking a strong stance on negiah with the immediate family would cause major issues of shalom bayit am I allowed to have limited physical contact with my aunts and cousins? Thanks, Ezra