Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Volume 18, Page 46-47, Fatwa No.20062, Question 3
Question: What is the responsibility of the walee (guardian) of a young woman towards a man who has come forth to propose to his daughter?
Response: It is obligatory upon the walee to select, for the one to whom he is a guardian over, a suitable pious man whose [practise of the] religion and trustworthiness he is pleased with, as he ﷺ said:
«When someone with whose religion and character you are satisfied with asks for your daughter in marriage, accede to his request. If you do not do so, there will be temptation on Earth and extensive corruption», transmitted by Ibn Maajah and at-Tirmidhee, who said the hadeeth is hasan-ghareeb.
So it is obligatory upon the walee to fear Allaah in this regard, and honour the best interests of the one to whom he is a guardian over, and not his own interests; Certainly, he has been entrusted with the responsibility which Allaah has bestowed upon him, and he is not to require of the proposer [to the young woman] that which he is unable, such as requesting mahr above the common practice (rate).
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet Muhammad ﷺ and his family and his companions.