Your question is very general. Help a complete stranger? Under what circumstances? What KIND of help?
In terms of offering a helping hand when someone is in the midst of crisis or disaster, giving of necessary items (food, clothing etc.) there should be little if any danger. This of course is speaking of being charitable. Let's hope we can all safely do this.
Other than this, it's probably safe to help a close friend or family member providing you love and trust this person. When it's someone close to you, you can pretty much know whether they are in serious need or just looking for hand-outs.
When it comes to strangers, quite sadly I think far too many horror stories have been related for me to jump blindly into helping to any degree. I hate to say this but the fact is there are scam artists everywhere. Their motives are less than acceptable and we are the only ones to best protect ourselves against these sorts of individuals. Once we've fallen for a fraud's lament, it's too late to be sorry.