When you are playing by a different set of rules, i.e., a lack of moral character, it is easy to sound more intelligent than you are.
Trust me, after spending almost half my life in the federal government by the time I left, I lost count of the people at first glance I thought were intelligent, but instead, were morally corrupt to the core. When you live a life of make-believe and are continuously dishonest, you are not a real person, but playing a character. In most cases a character far smarter than you actually are.
A perfect example of this was during protective details; we would run into Hollywood celebrities at many of the events we were working. Many, I was familiar with and had seen their tv shows and/or movies. I was dumbfounded on numerous occasions at how completely moronic these celebrities were in real life. But ironically, numerous had played character roles of brilliant people. I saw this same thing with politicians with whom I had even more contact regularly.
Unfortunately, the above is a key component of a sociopath. They are so good at lying and playing a role, you are easily duped into thinking they are something they are not.
There is no magic bullshit detector to weed these people out quickly. But a good rule is to pay attention to how they act, not what they say. Eventually, the true colors will come out, as they usually tell so many lies they usually trip themselves up. Another good piece of advice is someone who has to tell you how brilliant they are, usually isn’t.