The situation is not much different here in Brazil. It's almost impossible to tell when a beggar is telling the truth or not - they have perfected their story-telling out of necessity.

Once I was walking up to a friend's apartment. Just a few meters from his door, a guy with a desperate face approached and asked me to borrow some money for gas/something, so that he could get to his wife who was in the hospital (red flag). I refused, and then he proceeded to tell me the exact address he was going to, handed me his license and car keys to check. I felt ashamed for being such a cold person, and gave him ten bucks. Just as he was turning around the corner, my friend who was leaving his apt saw him and said -"did you give that guy money? He is always around" :(

Never gave out money since. I try to make up for it by being very straight about taxes and civilization in general.