The Grand Ayatollah Seyyed Sadeq Rouhani answered questions about high dowry.
Question: Is it allowed to demand high dowry in Islam? In your opinion, is there a solution for the girl and the boy who are willing to marry but due to high dowry demand by the girl’s family, the marriage is cancelled?
The Grand Ayatollah Rouhani: There is nothing wrong religiously with agreed high dowry, but the dowry which is set by the religion, is the dowry of Al-Sunnah (Dowry set by the Prophet (PBUH)) which is low and brief. If the bride is not satisfied with the dowry set by her parents, groom can agree with her that the dowry can be as it is (set by the parents) but after and at the time of registering the marriage with both sides agreement, the bride can give back the extra parts of the dowry to the groom as present.
source : Shafaqna