david,
It sounds to me like the LT-40 that guy has is set up with way too much throw on the controls. Either that, or he mis-understands how the controls work.
ALOT of people come in thinking they need to turn an airplane like they turn a car. As a result, then move the aileron stick to the side, and HOLD IT THERE to "keep turning". Before you know it, they are over-banked or even inverted, and heading for the ground.
Show the guy a hands-off climbing turn/spiral, it may help his brain learn how to turn.
He had help putting his plane together by a thirty year veteran that set all the controls and is the one trying to teach him to fly. I don't think it's the plane. I have an uncle who is a brilliant and successful businessman (wealthy). He is an intelligent man but he can't figure out how to change the tire on his car. If he has a flat in the middle of no-mans land, he has to wait for someone to come change it for him. His mind just doesn't work in a mechanical way regardless of how simple the task. I think the same is true of some people who decide they want to fly. The desire is there but unfortunately the coordination is not.