A few quotes from the Rabbi on 'Tzedakah and Healing'
in which he teaches that if one is exacting with the poor, one will never give charity in his lifetime
"If one watches the wind, he will never sow; and if one observes the clouds, he will never reap". For if a person is exacting with the poor, saying "This one seems worthy to be given [charity] and is not a cheat, this one is a cheat and I will not give him" - such a person will never give charity, for a human being sees into the eyes, while God sees into the heart. A person who appears worthy in your eyes may possibly be a cheat, while one who seems like a cheat to you may be a worthy person and not a cheat. This is similar to individuals who wish to sow their field yet remain on their guard in case the winds arrive and scatter the earth covering the seeds so that the seeds will not grow. Thinking this way will prevent sowing forever. Similarly, a person seeking to reap their field who looks for clouds in the skies every day, lest the rains fall on their harvest, prevent it from drying and ruin it, will not be able to reap because of these thoughts. So it is with you, O rich person. If you let this thought come to mind and say this one is worthy of being given and this one is not, you will never give charity during your entire lifetime. Rather, let no poor person who approaches you leave emptyhanded, and leave this issue in God's hands, who will consider it charity…
Ofrot Tevel, p.64, published by the author, London, 1850