a good Judge of character is able to guess the character of a person at first sight
the only related Italian expression I can think of is “avere intuito psicologico” i.e. “to have psychological insight/intuition”
“fisionomista” is people able to remember the physiognomy/face of a person; in a broad sense, people having psychological insight
from google:
fisionomista : Chi ricorda facilmente la fisionomia di una persona; anche chi sa riconoscere il carattere altrui dall'esame della fisionomia.
a related funny word is “lombrosiano”, Cesare Lombroso was an Italian doctor, known as the inventor of the so called “antropologia criminale” (criminology, see
http://www.criminology.fsu.edu/crimtheory/lombroso.htm or
http://en.wikipedia.org/wiki/Cesare_Lombroso ); lombrosiano is the adjective from Lombroso
now many people use the word ‘lombrosiano’ in a comic way:
Sono un lombrosiano convinto: il Tale è un idiota, basta guardarlo in faccia, con quella testa a pera...
(I’m an out-and-out lombrosiano: that dude is a perfect idiot, as long as you look at his face, with his pear-like head…)