You have time to stop and engage in a verification process? Just how does such a person prove that they are a veteran? Why are those who rampaged across Southeast Asia and assisted in the killing of hundreds of thousands in that region -- for no perceptible benefit to American security -- more deserving of your money than, say, persons who was on the cusp of poverty, lacked insurance, and lost their home in a fire?
Over the years, I've made small talk with some while getting coffee, waiting for trains, etc..... they'll mention VA appointments, show VA ID, mention various engagements, etc..... if I talk to to them a couple of times, and they seem legit they can have my change every once and a while. I also look at the general condition of a person, if they've lost limbs, sight, or are in general poor health, they, too, can have my change if they want it ex-service or not.
WWII, Korea, etc..... are not legitimate? I've known lots of poor vets from those Wars that have asked for help at certain times. And I quite frankly, don't care what they've done, most were young and doing what they thought was right in service of our country, and for that I give them a tad more respect.
As for people that are homeless due to fire, etc....... No, I have sympathy for them, and if one was to pass the hat for a person in that circumstance, I'd offer something, but in my experience people like that generally aren't homeless too long, unless there is some other issue going on.