A few quotes from the Rabbi on 'Tzedakah and Healing'
in which he explains the meaning of robbing from the poor who may not really be poor
The following verse, "Do not rob the poor because he is poor", requires an accurate explanation. Does it mean that robbing a rich person is permitted?! And is the reason robbing is forbidden because the victim is poor? Robbing is forbidden, whether the victim be a rich or poor person. Actually, this may refer to those people who, out of pity, say that a poor person is not really poor but just makes himself seem so. This is what is meant by "Do not rob the poor" – saying he is not really poor. For he really is, but you rob him of the title "poor" so as not to give him charity. This is only the evil inclination's incitement preventing you from fulfilling a commandment. It also seems to me that the meaning of Scripture in "that which was robbed from the poor is in your houses" is that when they come to knock at your door, they are rejected with claims of their not being poor and only making themselves appear to be poor – but they really are poor. And that which was robbed from the poor is your saying that they are not really poor… and you do not give them charity; by doing so you are robbing them.
Ohel Yesharim – Morals and Sermons, p. 71, Machon Haketav, Jerusalem, 1981