I used to volunteer for a local Welfare rights organisation.
We used to have homeless people come in for advice. I have known terrible cars of people with LD's, many who have come through the residential system who the Council deny they have a duty of care towards.
We luckily have local charities that have washing facilities etc. I had one man come in who was reagulary being attacked (beating up a person who was down on his luck was a fashionable pass time, as was pissing on them), we were sorting out his benefits and directed him to this service.
He came in a couple of weeks later, the difference was amazing. Many people "in the know", SW's, Nurses, Doctors etc donate top named barely worn clothes, so those who are homeless can be wearing deceptive clothing, as well.
This keeps them safe. We used to have them come into our office, we let them sit for a while, we would be happy to give them water (of course) there were three regulars that we let phone family occasionally.
There are gaps in the services, likewise some are street dwellers because of addiction, but again there are gaps across every service.
OP, decide what you want to give, that is your right, but don't assume that the person is genuine, in which case, it's a mater of knowing how to use money effectively, if he was a piss taker, then no thought needed.
There isn't any need the think so deeply about this one incident.