It seems to me that you can find out a lot about people's intelligence by talking with them a little
This only works with people less intelligent than yourself. Someone with intelligence comparable to yours who's good at smooth talking can easily convince you that he's much smarter than you.
I find that I don't agree with this comment, though perhaps if I thought about it more I would..
I often categorize people as 10-points-smarter-than-me, 20-points-smarter-than-me, etc, just naturally as I go about my day, and I'm (currently) fairly confident of my evaluations.
Sometimes I can get a pretty good estimate by speaking with someone for 5 minutes -- but I'm aware this is heavily weighted towards verbal acuity, which is just one dimension. A high verbal acuity for me is a marker of high IQ, though average verbal acuity is not strong evidence eithe...
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.