1) My question is that what are the rulings of mehr? Who gets to decide the amount of mehr and when and how much should it be given?
2) Who decides the amount of mehr? Who’s right is this?
3) On what basis or standards should the amount of mehr be fixed?
4) What if a girl’s father is adamant on asking for a big amount of mehr then what are the hadiths and rulings in this matter?

1) The girl can ask for whatever she likes for mahr but ideally it should be agreed between the man and the woman beforehand including when and how it should be given.

2) The woman has the right with consultation with her family and her spouse to be.

3) It should be in accordance with the society and social status of the woman.

4) Amir al-Mu’minin (‘a) has declared:

عن علیّ (ع) قال: «لاتغالوا بمهور النساء فتکون عداوة.»

Do not set substantial Mahr for women and do not compete in its excess for this causes enmity.