I always give a dollar to the first person who asks for it in any given day, regardless of whether I think they deserve. If they're asking for money, they probably need it. I don't think telling people they need it for bus fare is a scam, it's just another strategy.
My general experience is that people asking for money don't need it, not in the sense they'd starve without it anyway.
In the UK people asking for money straight out are usually drinkers. Drug users and scammers tend to want more than loose change hence the more elaborate stories.
I should add that I have been homeless and without money. One time my only option of eating was stealing food or asking for money. I chose not to eat.
I could walk you round a city in the UK and I could point out the real homeless and desperate people that you would never see - mainly because these are not the people asking for money.
I appreciate there is a huge difference here between UK and US since we have a welfare system that is many times more generous than yours. The people you encounter may indeed need the money?
You present "I chose not to eat" as if you made the moral choice. But there is no shame in asking for help if you need it. I don't have illusions about what most people asking for money are going to spend it on. Honestly, they have to deal with loneliness and destitution somehow. That is why I specifically say regardless of whether I think they deserve it.