Man oh man, Siberian... You could have read my mind. I had wanted to post a couple of threads about this very subject a few days ago but didn't have the time or gumption to do it, so thank you very much for posting this.
For those who don't like long posts, you might want to skip over this one...
Three days ago, I was approached by a man at a gas station asking me if I'd donate to his church's home for drug addicts. To tell you the honest truth, I hate being solicited while at public places, and I've almost always been approached by men, which automatically puts me on the defensive. To be honest, I was rather curt with him because, although he was polite, he was also very aggressive, seeing as he walked right up to my car.
I have sometimes reported solicitors and will often avoid places that are known to have them in their parking lots. One guy was even asking for money for his kid's soccer team, which I personally felt was really overdoing it.
Please note that I am NOT trying to say IN ANY WAY that all men are predators. But for me, it's usually been men who literally walk up to me while I'm at or in my car, so as a single woman who used to park a bit far away for the extra exercise (which helps with your 3rd question, Siberian!

), I automatically go into "defense mode" when a strange man comes over to talk to me. Back when I was in college (and it was in a "good" town), a girl was kidnapped at gunpoint from the parking lot of a grocery store I used to go to every week (at 2 PM in the afternoon), and another was nearly kidnapped from the parking lot of a coffee shop my friends and I had gone to all the time... So, I try to be cautious.
If someone I don't know is approaching me in the middle of nowhere, I try to remind myself to grab my phone and keys, just in case. In the back of my head I'm thinking, "Dial 911 and start shouting your location if something goes wrong!"
For me personally, I would never hand over my credit card information, and like Cinder, I prefer to seek out and research causes I want to donate to instead. In fact, I prayed a long time ago that one of the ways God would help me discern who to give to was to lead me to people/organizations that AREN'T aggressively going after people for money in this way. If I'm in a big city and see beggars, I usually carry a little bit of extra cash specifically for that purpose BUT I always choose to donate to the ones who are sitting back quietly and NOT getting up in people's faces.
I do have one situation that I'll always remember though. I was sitting in my car towards the end of a Target parking lot on a gloomy, slightly brisk fall afternoon, and a young guy came out of nowhere and rapped on my window. He told me he was new to the area, had been walking for 3 days without anything to eat, and could I please help him get a hotel room? To be honest, I was totally thrown off guard (and frankly, a little bit scared) by his boldness, and while I tried to be polite, I adamantly turned him down and drove away. The whole time I was thinking to myself, "Why does he seem so familiar?"
Several months later, I found out why. This young man's obituary was in the local paper, and I realized he was someone who had worked at the same place I did a while back. He'd gone to the local high school, and, at the time, some of the girls I worked with told me he was trying to get them to sleep with him even though he had a baby on the way with another girl.
He had also been known to have a lot of problems with drugs, and though the paper didn't give a specific cause of death, everyone who knew him said it was from an overdose.
Even though this was probably 15 years ago, I still look back and think of that afternoon and wonder if there was something I could have done to help. But when I pray about it, to be honest, I don't think there's anything I could have done, and I'm pretty sure, if I would have given him anything, I would have only been contributing to his issues.
I realize others might have reacted differently, but God might have asked something different of them in that situation.
This is part of what helped me come to a better sense of peace over whom I should and should not give to. If warning bells are going off in my head the whole time, I go with my gut reaction and leave. But sometimes, God does tap me on the shoulder. (I know someone will probably say, "You should keep what you do for others between you and the Lord!!!", but the reason I share stories is because I'm hoping that it will help others relate, and also sort through what they may be going through, too.)
Last Thanksgiving I was driving home from work and saw a woman standing in an empty parking lot with a sign for help. Something in the back of my head told me to turn around and stop. I could have just given it to her from my window, but something told me to park the car several feet away and make the effort to walk over to her instead. I gave her what I felt God was telling me to give, along with a hug. She had tears in her eyes, and by the time I made it back to my car, I did, too.
I don't know if there's something else I should have done. But, I feel that at the time, I did what God was asking me to do. However, I'm always left with a the feeling of, "What more could/should I have done?", and I have yet to answer that question.