Would you co-sign a loan with a family member who seems careless with money?

1.Would you be honest and tell them why you will no co-sign if they ask?
2.Or would you agree to co-sign knowing that payment will probably fall on you and that it could mess up your credit?
3.Do they have to be really close to you for you to co-sign or it doesn’t matter? Money is money, and family is family and the two should never mix.