Combine the tequila, mixer, liqueur and lime juice in a cocktail shaker with ice. Shake vigorously until combined.
If using salt, pour a small amount onto a rimmed plate. Rub the rim of each glass with a grapefruit wedge, then roll the rim of the glass through the salt.
Fill glasses with ice and pour margaritas over ice. Garnish with fresh grapefruit wedge.