I used to give money to anyone who asked, even when I had very little myself. I was taken advantage of a couple of time and now am more selective.
I was in London once and there was a lady begging at the entrance of a supermarket. I did not have any change to give to her as she was going on about how hard done she was, with little children she could not feed... I went to do my shopping and bought things I would have bought for my own childre: milk, cereals, fruit juice and some other bits and bobs for her, complitely forgot to do my own shopping. I got out of the shop, handed her a full bag of goodies and was absolutely flabagastered when she said to me ""so you have got change now?""
The other time was abroad, in a North African country. Out shopping with my SIL, there was a young woman holding what looked like a tiny baby all wrapped up in rags. SIL told me do not get fooled "she probably has more money than you." I just could not not give anything so gave her a bit of money I had on me, the woman then ran away leaving on the floor the "baby" which was actually a piece of wood. I am laughing about it now but did not find it very funny at the time. The morality to this story is to sometimes, not always...listen to your SIL!
Now when I see people begging, I ask them if they would like me to get food,soap, blankets...for them, if they only want money I just walk my way.