I read about a phony investment scam recently. This one didn’t even have the sophistication of a pyramid or Ponzi scheme. The pitch basically consisted of this: “Give us $800 now, and later you’ll get up to $3,000 for being an early investor.”

I’m not even sure how much detail it went into beyond that.

And sure, it’s easy to spot such an obvious scam…from the outside. But real people fell for it. There was something about the approach that sounded appealing and legitimate. I say it all the time: nobody is 100% immune to fraud.

Still, I wasn’t going to write a whole article about this particular scheme because there really wasn’t anything to write about, but it did make me think, “Is there some kind of basic rule that people can use to filter out schemes like this?” The victims were approached with an (alleged) investment opportunity that sounded good, sent their money, and never got a dime back.

And there it was: they were approached.

They weren’t looking for something to invest in. Somebody approached the victims, out of the blue, with the promise of large, guaranteed returns.

Large, guaranteed returns are suspicious enough, but think about how investing really works in the real world: unless you’re a venture capitalist, nobody is ever going to simply approach you out of nowhere with something to invest in. If you want to invest for profit, you’ve got to find your own opportunities. You can hire a firm to help, or strike out on your own, but there’s never really been a case where, “Hey stranger, give me money and I guarantee you’ll get all of it back, many times over, in return” has turned out to be a legitimate offer. People don’t just share money with strangers. They don’t even share it with friends most of the time.

So here’s your one easy rule:

Be very suspicious of any investment opportunity where you did not initiate contact.

This touches on affinity fraud, too, where someone will use shared membership in a group to build trust in order to sell fraudulent investments. This often happens in churches, where a member of a congregation will present materials relating to an investment that later turns out to be nothing more than a scam.

You can ask other questions, too. Is the person selling this investment licensed to do so? Does the offer make sense vis-à-vis how the world actually functions? Why are you, of all people, being given this opportunity? Are the promises being made just a little too amazing? Is the seller hitting the “I’m just like you” note a little too hard? Is there a shadowy, mysterious “they” that supposedly doesn’t want you to know about the investment? Are they talking about “guaranteed” returns?

All of these questions can help you filter out an investment scam, but if you stop at the point a stranger is making a too-good-to-be-true offer, you can avoid fraud from the outset. It doesn’t apply to every case (because nothing applies to every case), but it’s a pretty good start. If someone is presenting an out-of-the blue investment opportunity, that’s your first red flag.