To exploit an opponent's weakness in their backhand smash, you should focus on controlling the pace and placement of your shots. Start by hitting deep balls towards their backhand side to force them into a position where they have to execute the smash. Mix in high, arcing shots that push them back and create a challenging angle, making it difficult for them to commit to an effective smash. Additionally, vary your shot direction and speed to disrupt their rhythm; if they consistently struggle with the backhand, consider employing drop shots or cross-court angles to draw them in and expose their vulnerability further. Ultimately, maintaining strategic pressure while anticipating their movement will enhance your chances of capitalizing on their weaker shots.