How can she be
    sure of the Islam of a person whom she wants to marry?
Question

                Hello, my question is that I like a guy who
      is not muslim, but he is willing to change his religion. The problem is that he says he
      will do it, but if it dosn't come from the heart then it's not acceptable. I know that my
      parents will have a lot of friction with this guy because he is half black half white. I
      am afraid because I don't want to loose my parents even if teh guy changes his religion
      and becomes a true muslim how can I be sure that he will committ to it.
Praise be to Allah.You need to know, may Allaah help you to adhere firmly to Islam, that it
        is not permissible for a Muslim to love a kaafir, because Allaah says (interpretation of
        the meaning): You (O Muhammad) will not find any people who believe in Allaah and
        the Last Day, making friendship with those who oppose Allaah and His Messenger (Muhammad),
        even though they were their fathers or their sons or their brothers or their kindred
        (people). [al-Mujaadilah 58:22]
As you say that you love him, you have to give up this love for the sake
        of Allaah; whoever gives up a thing for the sake of Allaah, Allaah will compensate him
        with something better.
If this young man declares his Islam and you fear that he is not sincere
        in his Islam, remember what Allaah said (interpretation of the meaning): O you
        who believe! When believing women come to you as emigrants, examine them; Allaah knows
        best as to their Faith, then if you ascertain that they are true believers send them not
        back to the disbelievers. They are not lawful (wives) for the disbelievers nor are the
        disbelievers lawful (husbands) for them. [al-Mumtahinah 60:10]
So he could be tested by asking him about Allaah, His religion, and
      His Prophet Muhammad 
 (peace and blessings of Allaah be upon him), and about the religion
      that he claims to have left.
You could also make sure of his Islam by watching to see if he persists
      in the obligatory acts of worship, such as prayer  especially if there is a mosque
      nearby  and fasting.
If a person  especially a new Muslim  is really serious
      about Islam, this will also manifest itself in other ways, such as whether he bothers to
      ask questions about the rulings on halaal and haraam. 
He will also be concerned about changing the way he is, such as ridding
      himself of kaafir rituals and giving up things that are munkar and haraam that he used to
      do before he was Muslim.
Whether he is truly Muslim will also be seen from the way he hates the
      kufr that he used to follow before. The Prophet 
 (peace and blessings of Allaah be upon
      him) said: There are three things, whoever attains them will find the sweetness of
      faith: when Allaah and His Messenger are more beloved to him than anyone else; when he
      loves a person and loves him only for the sake of Allaah; and when he would hate to return
      to kufr after Allaah has saved him from it, as he would hate to be thrown into the
      fire. (Narrated by al-Bukhaari, 21).
We also want to be sure that there is no forbidden relationship, because a
      Muslim woman is not permitted to do this. She should not touch or be alone with a
      non-mahram man (one to whom she is not married or related by close blood ties). We ask
      Allaah to choose good for you and to decree it for you and to keep you safe from all evil.
      May Allaah bless our Prophet Muhammad.