You're in a bar meeting a few friends for a pint. An older gentleman sits at the other end of the table, but he seems harmless so you don't think twice about it. As the night progresses and so does everybody’s intoxication level, you find yourself chatting with him. He tells you he's an army retiree who has spent time in Iraq and Afghanistan.
After sharing a couple of his engaging but brutal war stories, he tells you he's going through a bit of a rough time. His accomplishments aren't being recognized as they should and he's too injured to work, while his pension is ridiculous low.
He also mentions a fundraiser he is working on for him and a few of his former comrades. He even pulls out a list with 20 or 30 other people who have already donated and he asks you and your buddies if you can hand over a few dollars to help out. These types of scams can pull in more money than expected since the victims are sympathetic and, often, drunk. Often times, they'll have more than just their bar tab paid for.
How to avoid: it's tough to be cynical about people but sometimes you have to be to avoid getting ripped off. Either find a way you can donate online or ask him if there are any fundraisers he's involved in. But if the only place you can donate is directly to a guy you just met in a bar, maybe you should save your charitable donation for another cause.