Makes you feel miserable
On a serious node:
I don't think it's easy to spot tells that he is top level unless you are toplevel youself. (I couldn't tell since I am novice myself)
But -
Doesn't do more than a few technical flops per match
Makes it look like he is committing and punishes the opponent's missed whiff punish or is able to know wether or not the opponent chose a safe whiff punish option
Has extensive MU knowledge (knows what to exploit and what to look out for in the match up, such as what they want to do in the MU vs Sheik and character specifics such as frame data including OoS options, favorable combo follow ups, edge guards and kill moves and the trajectories of those, thus knowing how to mixup your DI and or (A(SDI))
Can reliably power shield and shield drop
Has good reading comprehension (picks up on habbits)
Can react to different DI the opponent chose in combos
Knows when the opponent is/will be out of reach
Acknowledging when making bad calls
Does not hesitate/ hit confirms
Keeps composure when pressured/ behind in the match
Is still learning
And moonwalks across the stage on KO instead of charging needles