The din kul haposhet yad nosnim, applies on purim.
Not everyone has unlimited resources to write a check to everyone who stops them in shul, the street or knocks at their door. I give most of my maaser to my childrens yeshivos and the rest to the local tomche shabbos and/or masbia.
For those who go around in shul or the street I have available a large bag of change and try to give something (unless as noted above the person reeks of alcohol or cigarettes)..
At home, we have a jar filled with single dollars and anytime someone knocks on the door my children (those who we allow to answer the door) are instructed (if we are not home) to always give 2-3 dollars to each person.
My wife used to offer those collecting something to eat or drink, but after someone collecting plopped himself down on the sofa and wouldnt leave without a check for $180, she to is to scared to offer much more than the few dollars.
It is hard to say who is legit and who not. It is hard to determine who “really” needs and how much. With the exception of my nose test which I have never discussed with my Rav, I prioritize my tzedaka under the direction of my Rav.