My dad used to tell us kids that if something sounded too good to be true, it probably was.

I suppose every kid’s dad or mom or favorite aunt or great uncle or grandma or grandpa gave that advice at one time or another. It’s probably somewhere in the great Book of Parenting. I’ve never seen such a book, but one must exist. We all give our kids some of the same enduring, universal advice. It can’t just be oral tradition, can it?

(The closest Nancy and I came to a book about parenting was Dr. Benjamin Spock’s “Baby and Child Care,’’ which was pretty much a universal thing among young parents in our time, but that’s another story.)

Too good to be true is a sage bit of caution, and not just for kids. I’ve become a member of the older population in this country. We’re a demographic grouping that falls prey to scam artists and con men at a higher rate than the general population. That’s probably why so many warnings from consumer protection groups and attorneys general and other defenders of old people are directed our way.

I generally heed those warnings, too, although I confess I sometimes laugh when I read them and think to myself, “What fool would fall for that kind of a line?’’ That’s really unkind, because a fair number of rational, good-hearted and well-meaning people fall for scams and cons every day. People my age – and this is a generalization but kind of true – were raised to think the best of their fellow humans, to give others the benefit of the doubt.

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My generation might be the last one that grew up with the old saying “Fool me once, shame on you. Fool me twice, shame on me.’’ Former President George W. Bush once mangled that saying during a public appearance. He said something like “Fool me once, shame on – shame on you. Fool me — you can’t get fooled again,’’ and some people ridiculed him. When I heard it, I laughed, yes, but I confess it kind of endeared him to me, so there’s that.

I may have grown up giving people the benefit of the doubt, but these days I’m pretty suspicious of my fellow human beings. I never answer my phone if I don’t recognize the number. Never. It used to bother me, letting a phone call roll over to voicemail. For much of my life, the telephone was a combination of necessity and novelty. Calls were limited to work or medical or emergencies. When the home telephone rang, it was probably important. So not answering my phone wasn’t easy at first. Now, though, I see an unfamiliar number and I think, “If they want something, they’ll leave a message.’’

Lately, my phone calls have sometimes carried, instead of a number, a thing that says “potential scam.’’ That’s kind of unsettling, but I prefer it to a blank number. It makes me feel all righteous about not answering “potential scam.’’

A close friend recently got a call – bad connection, hard to hear the voice – from someone who said he was the grandson. The bad connection made it difficult to recognize the voice, so he said the name of one of his grandsons. The caller said, “Yes, it’s me. I’m in trouble.’’ After another minute or so, my friend became suspicious, hung up and called the grandson’s parents, who had just talked to the kid in his college dorm room.

Now, I might fall for a thing like that, what with my terrible hearing and love of my grandchildren. Better if I don’t answer the phone at all. (If you’re calling and I don’t answer, sorry, leave a message.)

Just the other morning, I passed up a too-good deal. I’m looking for summer shorts, end of season bargains, you know. I saw an online ad with a good-looking pair of shorts for $39. I hit the “shop now’’ button and learned the shorts were marked down from $239.94. Whoa. Marked down $200? Way too good to be true, right?

I closed out the page and opened an enlightening internet discussion of politics.