It is so hard to tell what is a genuine need, isn't it? I have to confess I usually walk past the beggars outside supermarkets, though I do usually try to acknowledge their presence with a smile. If I offer them a hot drink, they usually say someone has just given them one.
But on one occasion a young lad sitting by the entrance somehow didn't look like the usual type. He called out to me for help and said his girlfriend has just kicked him out with nothing and he needed a few pounds more to make up the train fare to get back to his parents. Something just nudged me that he might actually be telling the truth, I don't know why, and with some hesitation I did give him £5. He was extraordinarily grateful, thanking me over and over again, and got up and walked off. I had to return a few minutes later, and there was no sign of him, so I really do hope he made it home! 
I am always conscious of the instruction 'As you did it to one of the least of thesemy brothers, you did it to me' and feel that I fail in that regard so often!