What is the ruling on the deferred mahr, who determines its amount, is it determined by custom and capability, and how should a young man act if his fiancée's family demands an excessive deferred mahr?

The jurists have agreed that there is no maximum limit for the sadaq (bridal gift), based on the Almighty's saying: "And you have given one of them a qintar" (Surah An-Nisa, 4:20). Its amount is determined by the agreement of the spouses and the woman's guardians. If the sadaq is not mentioned at the time of the contract (delegated marriage - nikah al-tafwid), then its determination is based on custom (sadaq al-mithl, i.e., the customary bridal gift). The sadaq can be paid in advance or deferred, either in full or in part. Reducing the mahr (bridal gift) is better than exaggerating it, as it conforms to the guidance of the Prophet, peace be upon him. The woman's family should be persuaded to lighten the mahr, and righteous and virtuous people can be sought for assistance in this matter.