Who is a Poor Person Worthy of Receiving Charity?
How can we determine who deserves our charitable donations in modern times?

The Gemara in Bava Kamma (page 16) relates that the prophet Jeremiah suffered greatly from the people of his generation, who refused to accept his prophecies about the imminent destruction of the Temple. As a result, he prayed to Hashem to send them undeserving poor people, so they would not merit the great reward for the mitzvah of charity. Maharsha (Chiddushei Aggadot) explains that since the mitzvah of charity protects a person from punishments they might deserve for their evil deeds, as the verse states (Proverbs 21:14) "A gift in secret subdues anger," Jeremiah sought to prevent them from performing this mitzvah so they would bear the punishment they deserved.
Who is considered poor? The Mishnah (Peah, Chapter 8, Mishnah 8) explains that a person who possesses two hundred zuz, an amount sufficient to live on for a year, is not considered poor enough to collect gifts for the poor, gleanings, forgotten sheaves, corners of the field, or charity. Today, the value of two hundred zuz amounts to only a few hundred shekels, and if we were to determine poverty based on this amount, we would hardly be able to fulfill the mitzvah of charity, as virtually everyone possesses this sum. Additionally, the poor of our generation do not go out to the fields each year to collect gleanings, forgotten sheaves, and corners as the poor did in earlier periods, so their source of livelihood has diminished over the years.
Indeed, the Shulchan Aruch (Yoreh Deah, Chapter 253, Section 2, see "Biur HaGra" note 6) rules that since in our times the practice of gifts to the poor is not common, anyone who lacks money for their basic livelihood is considered poor and may receive charity. According to the poskim, even a person who has enough money for food but has no place to live may take from charity for housing needs (see Rambam, Laws of Gifts to the Poor, Chapter 7, Law 4, and also Responsa "Chatam Sofer" Yoreh Deah Chapter 239, Responsa "Minchat Yitzchak" Part 8, Chapter 72). Throughout the generations, the leading Torah scholars of each era deliberated and determined what amount was appropriate for minimal sustenance. We find an example of this in the Responsa of the "Chatam Sofer" (ibid.), regarding a fire that consumed the houses of an entire town, where the Chatam Sofer specified in detail who qualified as poor enough to receive charity: "We estimated according to the place and time, anyone whose livelihood depends on traveling and circulating through villages and towns - a sum of 200 gold coins in cash is sufficient for him to support himself."
Who is an undeserving poor person? Now that we know who is considered poor, we need to understand what the Gemara meant when it spoke of undeserving poor people. The authors of "Gilyonei HaShas" and "Meromei Sadeh" (in Kiddushin 36) explain that an "undeserving poor person" is not only a wealthy person pretending to be poor, but also a poor person whose behavior is improper. However, regarding a poor person whose conduct is improper, Rabbeinu Yonah (cited in Gilyonei HaShas) wrote that although one who gives him charity does not receive great reward, they do receive a small reward. For this reason, the author of "Meromei Sadeh" explains that Jeremiah asked Hashem to cause charity givers to encounter people pretending to be poor, so they would receive no reward at all.
The wisdom of the Rabbi of Brisk: It is told about the Rabbi of Brisk, Rabbi Yitzchak Zev Halevi Soloveitchik, that once someone asked him for charity and was met with an absolute refusal. When the charity collector left, the Rabbi's close associates inquired about his behavior toward the poor man. The Rabbi replied that the man's brazenness was evident on his face, and it is written (Proverbs 18:23): "The poor speak with entreaties, but the rich answer with impudence."