remit

I have few questions regarding Mahr. Many women (including my mom and sisters) back home in Pakistan forgave their husbands the Mahr on the first night of their marriage, because their husbands ask them to. My questions are:1) Can a woman forgive the man of her Mahr, if he says that he does not have the means to pay it or seeks forgiveness just so he can to get out of it (not pay it).2) If the answer to the above question is "yes", then can she demand it later at the time of divorce? Also, in this case isn't this a tricky way on the part of the husbands to deprive their wives from their rights making use of their shyness to ask for their rights. Will the money taken this way be lawful for the husband keeping in mind that the wife may have forgiven it out of shyness and the Prophet said this is unlawful? Thank you.