You should be able to tell something like that is fake just by looking at the way people on it are moving. It's really hard to get the physics exact, so it ends up looking somewhat funky. Even if such a thing doesn't really exist, you should have some idea of how the motion would look if someone were on a floating skateboard.
But I'm always surprised at how fake something will look, and there will still be people who believe it. Apparently it's all in the set up. It doesn't matter how fake something looks, if the delivery of it is realistic, there will be people who believe it.