What I know about sculling (topping) a shot is pretty much about three problems. Raising the head up, swaying, or other wise raising the arc of the swing with other body parts.
If the golfer raises their head up to a point that the head also brings shoulders up, the fix is to focus on keeping a steady head. If the golfer can keep the distance from their nose to the ground the same through out the down swing, they won't lift their head.
Raising the head up can also be attributed to straightening the knees, raising up at the waist, or even lifting the shoulders. A bad ball position can cause a "sort of" topped shot. A bad ball position is an easy fix. Just move the ball back in the stance a little, towards the low point of the swing. Google "brushing the grass in golf" for a tip.
I hear a lot of folks tell a golfer he raised his head, when actually all he did was turn his head, after the ball has been struck, to see where the ball is going. Most of us do this. That to me is not raising one's head. It's also possible to raise the head up, but not raise the shoulders. If the shoulders are not raised, the golfers swing arc does not raise, unless the golfer bends their elbows, or straightens up at the knees. Now if the golfer raises his shoulders up, then of course their head will raise too.
So if the golfer is bending their elbows before impact, that will raise the swing arc. Easy fix. Focus on keeping the elbows extended as they were at the address, and take away positions.
Straightening at the knees will raise the swing arc. Straightening the knees in the down swing, lifts the rest of the body, including the shoulders, which lift the arms and hands. The hands will lift the club head. The fix is to focus on keeping the posture as set at address, and take away positions.
Lifting at the shoulders is (IMHO) caused by trying to swing too hard, which causes tension. The golfer is looking at shot they are unsure of, maybe in between clubs, or anything else that makes them tighten up for a troublesome shot. The best fix I know of to fight tension is to focus on the same nice, easy swing they normally have. Myself I tend to practice on troublesome shots when ever I can so that I am not surprised on the course. My pre-shot routine also helps to stay lose in my swing. Tension was the main reason I topped shots until I made a change in my club make up.
If the golfer sways too much, that changes the swing arc by moving it either forward or backwards depending which way they sway. The low point of the swing changes. If the golfer sways to the rear in the back swing, with out swaying forward in the down swing, the low point of the swing will be behind the ball, and the club head will contact the ball on it's up swing, which is usually above the equator of the ball. This is what happens with a metal wood topped shot. With an iron which is usually on a steeper down swing, the club hit the top of the ball. The fix is to either not sway too much backwards, and if you do, don't forget to sway the same distance forward.
Take this info with a grain of salt as it is all I know, and understand about topping the ball.