I've struggled with that also - not knowing who is truly in need - but over time have concluded that any person who finds it necessary for any reason to be standing on the street begging clearly has some problem that prevents them from functioning in a way that most of us might consider normal and are thus deserving of compassion and help.

Now does that mean I'll hand them cash? Probably not; heck, I'd be broke before I got past more than a handful of busy intersections. But I can give to and support those organizations that do provide direct assistance as well as those organizations and politicians working on the root problem.