Are Mensa people really that smart, or are they just really good at answering useless questions and passing tests?

That is the fascinating infinite regress problem with IQ tests.

The testers ask questions and claims they are of interest to intelligent people. Then they claim answers that an intelligent person would give.

How do the testers know that their questions and answers are any good? Well... they're... intelligent. Because... they... took the test??

No! People just started off thinking they were smart for some reason and then devised a test to see HOW MUCH YOU THINK LIKE THE TESTER! That's all the IQ test tells you.

So, are the test makers smart? Are they only smart from some certain perspective? Or are they just full of BS??

The only answer to whether someone is smart or not is how you choose to evaluate them (and the process you use can be evaluated the same way).

What criterion should you use?? Well... that's the deep question. From a pragmatist standpoint, I judge intelligence by how well a person demonstrates understanding of a novel situation by being able to manipulate it to a desired result... how practical they are when outside their normal experience.

But... Albert Einstein supposedly went to a party without his pants on!! Either he had a weird sense of fun... or he REALLY SCREWED UP IN A SOCIAL CONTEXT!! I think he did.

So... I'm inclined to believe that there are many different types of being smart... and one can be smart in one way and dumb in another. Or, if they're lucky, smart in many different ways, and dumb in a few other. (And... conversely... some are just dumb in every way. You've met them, I know.)

Intelligence is a amorphous subject given to all manners of philosophizing, so read what people say... think... and come up with something that works for you in the world. (My pragmatism rearing it's head again.)

But not to worry... because, though intelligence is a wildly complicated philosophical subject... you can recognize stupid every time!