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.
You say not exactly, but you seem to be agreeing and clarifying?
Also there are definite strongish conscientiousness signals, such as education level and grooming/dress.
I think this post could use more context. Your point seems interesting and novel, but I'm not 100% certain what it is or what question you're trying to address.