All intelligence tests do is simply measure what some researcher's opinion of intelligence is, for how can anyone arrive at an indisputable & precise definition of the term? One may as well invent a Snark detector (Lewis Carroll, q.v.).
There is also the problem of sampling; how do we know the IQ will measure the same when repeated (if anyone even does this), & if it varies, which number is definitive? And if we choose to average them, how do we justify this over the maximum, minimum, median, or the mode? Incidentally, this is the same problem *all* quantitative scientific experiments have - measurements are selected & processed using arbitrary methods.
And more practically, how does the IQ translate into academic & professional ability? Perhaps a high IQ person is also a lazy slob (aka "bludger" in Australian).