Street scams are everywhere. And they all prey upon your wanting to be "nice" and your desire to help people.
Whenever someone approaches you on the street and says "Excuse me, sir.." or "Excuse me, ma'am..." chances are, you are about to be conned.
Usually they have a story to tell, long-winded but compact, of broken down cars, or running out of gas. The car is blocks away and they need a few bucks for gas or repairs. And if they don't get it soon, they'll lose their new job as courier! Or the kids in the car will get cranky! Or they will be AWOL from the Army base!
And so you give them a couple of bucks and go on your way. And an hour later, you walk by the same intersection, and the guy is still at it. And someone else has their wallet out and is giving them cash.
In most cases, it is a pretty low-level scam. The most you lose is a couple of bucks. But such people can be dangerous. People have reported being kidnapped by such folks, when asked for a "ride back to their car". And also wallets and purses have been stolen from vehicles on the pretext of such "rides".
And many such people, when you refuse to give them money, will either scream at you or even assault you. They are not very nice people, even though they act so sweet when telling their "story".
A variation on this is when two scammers work in a team - one to distract you with the "story" while the other takes your purse or wallet or other valuables out of your car.
And the props they use go beyond the gas can. Some even use children!
It is a bad idea to give these people money? Yes, it is. Because if you give them money, they will continue to do their scam - it is profitable for them. Just like drug addicts who pose as "homeless" to earn crack money, these scammers continue to scam because you can make a lot of money doing it.
If you are in doubt and actually believe these stories (and they are so similar, so why should you?) offer to call the Police on behalf of the person. In most cases, they will walk away quickly.
But frankly, I would advise against even that. These are criminals, period. And if they get within arm's reach of you, they can snatch your wallet, purse, or other valuables, and also hit you or otherwise injure you. And getting "in your face" is one thing they like to do.
Walk away - run if necessary - get to a safe place, cross the street, go to where there are more people. If you are in a mall or store parking lot, report the scammer to security, so they can chase him off the premises.
But don't give them money!