When Not To Trust Strangers

I had an interesting talk with my father about the case of con men. He mentioned one about a motorcyclist who offered to help a driver find direction using the driver's phone, only to speed away with the phone moments later. 

In our discussion, we agreed that as a rule, the friendliest strangers on the streets are those least to be trusted. This is because, normal people treat strangers like strangers. It is acceptable to smile and greet politely at strangers, but it is not normal to let them use our phone. It is fine to talk about the weather, traffic, or home-town, but it is not normal to share our home address. 

But it's not that strangers should be treated poorly. It also doesn't mean that, as a rule, we should never let strangers use our phone or tell them our full address. Obviously, there are exceptions to such rules - when someone desperately needs our help. And the trick to remain safe - while being helpful to strangers - is actually to trust them. 

The problem is not that we trust strangers too easily. The problem is that we don't trust them enough. 

Yes, we should learn to trust those we've never met before. If we really trusted the man on the street, we would be less vulnerable to those who try to cheat us. This is because by trusting the man on the street, we will find it normal to be awkward at first meeting. And so if somebody is getting too comfortable with us at the first meeting, we would be careful with him.

If a stranger asks for help or offers one, but hesitantly or shyly so, then he is the one we can trust. He is hesitant and shy because he is a stranger to you, and you are a stranger to him, and it is normal to be hesitant and shy to strangers. And because we trust strangers we can trust him. 

On the other hand, if somebody asks for help or offers one, all-too-readily as if he is our friend (when he is not), then we cannot trust him. He is neither a stranger (as he acts all-too-friendly), nor is he a friend of ours. We don't trust him because we only trust our friends and strangers - and he is neither of them(!)

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So to answer the question in the title, when not to trust strangers? Never. Although, apart from our friends and (real) strangers, we should trust no one else. That is, we can trust our friends and strangers; but we cannot trust friends who act like strangers, or strangers who act as if they are our friends.