'good insight into character'

Hi everybody,

1. How can I characterise a person being good at recognising others' character?

For example: you get to know somebody and you recognise them as a kind person. Later you will find them an evil person. If you do it in sequence then you are bad at recognising others' character.

I would like to find an adjective expressing that you are good/bad at recognising others' character (if any).

2. I have another question here:
http://www.EnglishForward.com/English/AtWeekendsWeekend/bgnbhj/post.htm

Thanks for your answer(s) in advance.