Usually, after taking the second or third 9mm to the gut, I start to thinking this guy just might be trouble.
Seriously, I think life experiences play a large roll in one’s ability to smell trouble. Intuition is part of it, but I think mostly intuition is developed by and reinforced with experiences. LEOs gain lot’s of experience dealing with trouble and the ones that are good at it live to tell. I think I’m pretty fair at it (gotten me around or through a lot of crappy situations anyway) and got there through non-LE life experiences.