There are a certain category of scams that prey on a personality trait that most of us have to some degree: greed. Some of us keep it chained up better than others, but on some (hopefully, deeply buried) level most people are a six-year-old who doesn’t want to share his/her birthday cake with anyone.

Hey, I’ll grab the last cookie without offering it to anyone else, too. If nobody’s looking.

But when it comes to con games and scams, not being greedy (or at least keeping it under wraps) can help you steer clear.

For example, let’s say you’re walking to your car when two people approach you. They tell you they’ve found a briefcase with a whole bunch of money in it, and they’re offering to split it with you. There’s always a complication, though, and they’ll ask you to provide some “good faith money” to throw in with the found cash. At this point, you’re supposed to withdraw a couple thousand dollars and hand it over to strangers. This is where being greedy—wanting to get something for nothing—will lead you into falling for a pigeon drop scam.

Look at all the “make money online” scams (some of which are so sophisticated they have their own late-night infomercials). You’re enticed with the promise of thousands of dollars per week (or even day), and all you have to do is send in your payment, sit back, and let the cash roll in. Again, you’re being greedy. You’re trying to get paid while providing zero value to anyone, and in the end you’ll be the one who loses.

Con artists and swindlers are nothing if not well versed in human nature. They know all about that inner Daffy Duck (“I may be a craven little coward, but I’m a greedy craven little coward”) lurking just under the surface of so many of us.

The reason they know all about it is that they’re giving it free rein over their own lives. Almost everyone has a weakness that can be exploited under the right conditions, especially when they’re not paying attention. When you find yourself in a situation, ask this question: “Am I trying to get something for nothing here?”

If the answer is “yes,” you might be gearing up to fall for a scam.