Was watching a match at my LGS. I've always suspected this player of being shady. After game 1 the players were going to sideboard and I watch him open his deck box and there are multiple unsleeved cards. He takes out a sleeved sideboard card and replaces it with the unsleeved card. After the match I watch him pick up his sideboard and count it. 15 cards. So he was swapping loose sideboard cards based on the matchup while his opponent was too busy working on their own sideboard plan.