The homeless can get first shot at charity dollars when they look appropriately piteous or charm passers-by. (Photo: Marc Levy)

Cambridge Day is part of a project called Voices of MainStreet — a weekly, nationwide Q&A in which editors at the money and lifestyle site MainStreet.com ask questions and bloggers answer them. For this entry, I was asked about charity.

The most affecting pleas for charity are the most direct ones, and they’re the ones I fall for almost constantly. It helps to learn how to weed out the scams.

It only took me what seems like several dozen lessons to develop a sense for them — maybe the last time was when I finally looked at the set of keys some guy had left me as security for “borrowing” $10 to do something that did something that let him get his wallet back so could buy gas for his car so he could get back home … to his cancer-stricken wife … and polio-ridden kids … and put out the fire about to consume them. And to the letter that had to be mailed before midnight so the bank wouldn’t repossess his house.

The key ring held the most random, absurd assortment of nonsense you could imagine: tiny keys to lockers or lockets, skeleton keys to houses that had probably been torn down decades ago.

This particular con man must have gotten some sort of charge out of gambling no one would look at the keys until he was out of sight; they were totally implausible.

But that never held me back from handing out my spare change, quarters or dollars, whether for a copy of Spare Change or if someone simply looked appropriately piteous (or charmed me enough). Even when I was unemployed I gave out too much money. Even when I was a student, living within a budget dwindling dangerously low as a semester waned.

In fact, once when I was a student I sat down and calculated how much money I was giving out, and it was high enough to startle me into vowing to cut back.

It’s simply difficult to walk past someone you can see, hear and even smell knowing you can make a difference in their lives that very day — possibly even that same, below-freezing night. Even when it twisted my gut knowing they were about to take my money into a grocery store with the intent of getting drunk on Listerine or vanilla extract, I found it hard not hand over a bit of change with the thought, “Well, what’s the alternative? Put him up at my place?”

The same set of calculations and rationalizations talks me out of contributing to larger causes such as natural disasters in Indonesia, Haiti or Japan. It’s the amount of money I have minus the amount I hand out on the street (donations to Goodwill, which cost me nothing in current income, don’t factor in) compared with the realization there is always a huge natural disaster happening somewhere added to the understanding that these huge expenses should be handled by foreign aid to which I already contribute as a taxpayer added to the fear my direct donation will go to a charity CEO’s private jet versus the realization that there are always, and will always be, homeless people needing my spare change. And lately, the sheer number of people on the street has brought me back to that disturbing moment in college: Added up, that’s a lot of money I’m giving away.

Still, the more I spend on myself – an amount that’s picked up with my own employment, of course – the more guilt I feel for not handing it out.

So there’s no subtraction going on, and actually more addition: My pique over politics in Wisconsin actually inspired me to donate money, and because of a nonsensically stubborn belief politics shouldn’t be about money (sort of like insisting chocolate shouldn’t be so fattening) I almost never donate money to such causes. I also intend to send pledges to the National Public Radio shows I’ve been freeloading on for years.

As bad as I am at math, I know the sum total of all this calculating is less money for me.

So I’m at least hoping that those earlier lessons have paid off. In other words, these days, I hope my scam detector is working better. Before handing over any money, I look at the keys.