Re: spot the difference
I think you'll find out it's the ones who THINK they are better than average go contracting. Or ones who don't care (know they don't care) and so will do whatever is needed to land a contract and then move on when they've sunk that job and get another.
Out of the ones who think they are better than average, maybe half actually ARE (90% of drivers think they are better than average...).
But unless you're quite selfless and VERY professional, you don't have the care that a permie does: when your contract ends, whether good or bad, you don't have to clean up the mess.
Being stiffed by your agent is slightly more common than being stiffed by your permanent employee, but not a whole lot.