Om Swami
Should I give money to a beggar if I don't know what they will do with it?
Don't refuse to give altogether
Giving without knowing where the money goes is called tamasic daan by Krishna. Still, it is not okay to not give at all, because at least a portion of what you spare will go to somebody.
Don't turn somebody away completely just because you don't know where your money will go. It's okay not to give in a particular case, but it's not okay to not give at all.