The role of the Wali or guardian has to be filled with wisdom, kindness and love for his daughter or ward, and no personal gain should enter into it :
All of the following hadith guides one into this aspect of the character of the Wali.
Narrated Saburah ibn Ma’bad al-Juhani:
The Apostle of Allah (peace_be_upon_him) prohibited temporary marriage with women.
Book 11, Number 2080:
The Prophet (peace_be_upon_him) said: There is no marriage without the permission of a guardian.
Narrated Abdullah ibn Umar:
The Prophet (peace_be_upon_him) said: Consult women about (the marriage of) their daughters.
Narrated Abdullah ibn Abbas:
A virgin came to the Prophet (peace_be_upon_him) and mentioned that her father had married her against her will, so the Prophet (peace_be_upon_him) allowed her to exercise her choice.
Book 11, Number 2088:
The Prophet (peace_be_upon_him) said: An orphan virgin girl should be consulted about herself; if she says nothing that indicates her permission, but if she refuses, the authority of the guardian cannot be exercised against her will. The full information rest with the tradition narrated by Yazid.
All of the above Ahadith are from :Translation of Sunan Abu-Dawud, Book 11:
Marriage (Kitab Al-Nikah