First of all, all of these “collectors” are NOT TZEDAKAH !
Many of them are collecting for themselves. They are perfectly capable of working, yet find it easier to schnorr. that is what they are SCHNORRERS.
IF they have a valid letter from an ESTABLISHED VAAD, that is NOT EXPIRED, then IT IS TZEDAKAH.
Many of these Russians come around with letters from a Rav in Queens that states IF you believe the are Jewish, then give them.
with regard to the Chadishe guys that swarm into shul and wave their hands under your nose, they should know the Halachas and know when they can or cannot collect. fi you ignore them, they will learn.