Does he pull when you are leading, dawdle, forge ahead? Get too close, or too far away?
Does he stop the instant you stop walking? Follow your pace when being led?
How is he when being groomed? Being fed? Being tacked? Being asked to give ground either when backed, or asked to swing? Ears forward and has a willing attitude, or is horse pissy about all of it?
And this has nothing to do with trust. Period. Horses don't worry about trust, they want a leader who they follow. That leader earned that position by being the one that can win the battle for supremacy, through attitude, or being willing to dish out HCTJM.
Horses make me a better person.