> Have you ever had a hard time figuring out if someone is really bright or not?

How do you define bright? Assuming bright to mean able to achieve post-grad honors:

I feel like you could easily distinguish if someone is bright or not within a few minutes of chatting.

I think that regardless of the subject of discussion, there are a number of strong indicators in the way a person speaks. One example is confidence: very rarely have I met a person I'd call intelligent that is also absurdly confident in their beliefs.

I realise my above statement is highly interpretable. What I mean is intelligent people seem to allow for their assumptions to be flawed, and be open to being proven wrong, about stuff that they can be proven wrong on (i.e. belief about a mathematical postulate versus belief in an objective truth such as global warming is real).