I don't know how useful this information is, because it's purely my opinion.. but, besides 'experience' and 'open mind' that are two pretty obvious ones, there

I don't know how useful this information is, because it's purely my opinion.. but, besides 'experience' and 'open mind' that are two pretty obvious ones, there are a few things I always look for and probably just as many that are unconscious; * What they are motivated by [the motivation itself gives you clarity in their personality. Lack of motivation does as well. None are bad traits, they just reveal things] * Posture and body language * Eye contact and eye movement when speaking * How they speak of other people, good and bad * Lying [everyone lies. some people lie about important things] * Reaction to criticism/blame * Evidence of perseverance * Dealing with silence [some people call them 'awkward silence'. That's pretty revealing ;D] * Balance of aggressiveness and passiveness * Ambition or lack thereof [no right or wrong here] * Levels of child-like enthusiasm for passions versus task driven enthusiasm * Social interests [again, unsocial introverts aren't necessarily a 'bad' trait. Just something that adds to your personality] * Instability I just wrote those up then, it's hard to verbalize, admittedly.