It's so fascinating to read about people being correct with their gut instinct about people. I've never been good at that, so I have had to find alternate ways to use discernment to become a good judge of character. What I look for is consistent behavior. I usually use my mistrust of Fe to identify people who seem too nice or too good to be true. But doing this from the beginning just escapes me. I love the way you all have expressed how you do this. It's like looking at the world through a completely different lens, but that lens makes sense to me.
One thing is very striking to me. When I have a really good first impression of someone I tend to be more mistrustful vs someone I have a neutral or negative impression of. I think I figure that if I can identify faults in that person, then that person is somehow more safe because they're more honest and put their cards on the table.