I was cured after I naively gave money to a street beggar, and was pursued for more money, to the point that I felt threatened.

My usual procedure in the US is to actively pretend that beggars, and those who look like them, don't exist. Phil Collins wouldn't like it, but after that occasion and one or two like it, I feel scared. I truly admire a certain friend who can chit-chat on a friendly basis with a street person.

As I got older and more confident, I developed other practices:

1. Someone asked for money for food, so I handed her a bag of fancy chocolate almonds I had in my hand. She looked like that wasn't what she was expecting.
2. In a friendly way, I told a collector for some ineffective charity that, in honor of his request, I would give 100 NIS more than usual to my regular charity, but not his. Chutzpah.
3. When a collector for some ineffective charity comes up to me, I solicit him, in a friendly way, to give money to my favorite charity before he has a chance to ask. Once I got 1 NIS this way, so I felt obliged to give him a (different) shekel. I then had fun ceremonially taking that 1 NIS coin to the treasurer, along with my usual donation.
4. Once I asked a phone collector for some ineffective charity, in a friendly way, to decide on my behalf: Should I give 100 NIS to a certain truly worthy cause, or deny it to that worthy cause and give it to her charity. She got quite tangled up trying to answer.

In short, I became a little obnoxious. The fact that I regularly give a good amount to charity is probably what gave me the psychological leeway to do this.

(And I wouldn't do any of that to a more-or-less worthy charity, or if a friend asked.)