The waiter rule works - if someone is rude to a waiter, it's an incredibly bad sign, because at the very least, it means they've never heard of the waiter rule.
However, just because someone is nice to a waiter doesn't mean they have good social skills or don't treat inferiors badly. It turns out there's an even better variant of the waiter rule: listen to all a person's interactions with other people. Listen, for example, to how that person talks about other people behind their back. As the aphorism says, what people will say to you about other people, they would say to other people about you.
In my real-life example of this lesson, there was a person who always gloated about how they had screwed or were about to screw other competitors, negotiators, etc, but of course always made sure to point out how much he was helping me. I foolishly believed it, when of course all the evidence was that I shouldn't. Eventually, the situation changed, he didn't need me anymore, and sure enough, he took advantage of me too.
Knowing how people treat others is supremely important as a defense mechanism.
A corollary to this, always speak in private as you would in public. Never say anything about someone else you would not say to them directly (even if you're talking to your spouse about work issues whatever). Sometimes you think you need to, but looking back it's always better to keep your own voice strong and true. It's like playing a violin. The more wrong notes you hit when you practice in private, the more wrong notes you hit when you perform in public. Eventually the bad notes resonate so much they start affecting the voice of the instrument and it starts to develop poor tone in and of itself. The wood particles start to re-align themselves. That's what separates the great instruments from the cheap instruments. Sure the great instruments were made well to start, but they were also played well throughout their lives. Always speak in private as you would in public.
This rule applies online too. Try not to make statements online that you're not comfortable seeing on the front page of the New York Times tomorrow, or indeed in 20 years.
As a general rule of thumb, you should always take a person's actions as a whole when you can. Unfortunately, you don't always have the luxury of getting to know someone well before making a major decision of some kind (for example, hiring someone). Sometimes you have to rely on these kinds of techniques. Not because they're foolproof (lord knows they aren't), but because they're all you've got.
Corroborating data point: A few jobs back, a contractor bragged over lunch about smuggling large amounts of spirits through Norvegian customs on his holidays. A week later he was found out lying about the hours he billed and promptly fired.
However, just because someone is nice to a waiter doesn't mean they have good social skills or don't treat inferiors badly. It turns out there's an even better variant of the waiter rule: listen to all a person's interactions with other people. Listen, for example, to how that person talks about other people behind their back. As the aphorism says, what people will say to you about other people, they would say to other people about you.
In my real-life example of this lesson, there was a person who always gloated about how they had screwed or were about to screw other competitors, negotiators, etc, but of course always made sure to point out how much he was helping me. I foolishly believed it, when of course all the evidence was that I shouldn't. Eventually, the situation changed, he didn't need me anymore, and sure enough, he took advantage of me too.
Knowing how people treat others is supremely important as a defense mechanism.