IQ is a pretty good measurement of how well someone takes an IQ test. Beyond that - there’s a big warning sign that should pop up when testing for something that has no agreed upon definition. The idea that IQ is a measure of “intelligence” is pseudoscience.
I've never heard of anyone saying "I thought that person was really intelligent, but they turned out not to be", and when there are scandals about people with fake credentials, they don't seem to come from people with fake credentials making mistakes-- instead, someone checks the history.
It seems to me that you can find out a lot about people's intelligence by talking with them a little, though I've underestimated people who were bright enough but didn't present as intellectual.
The real problems are with identifying conscientiousness, benevolence, and loyalty-- that's where the unpleasant surprises show up.