“It’s probably Matt Mercer’s fault.”
I've never struggled with this, but we all have different experiences with the game.
I'm curious what you mean by "never struggled with this". Meaning, like @iserith, you don't worry about it? Or you don't find it difficult to know when a player is using player knowledge? Or it doesn't happen at your table?
EDIT: Nevermind, you answered it in a subsequent post.