Put the honeydew in a blender and blend until smooth.
Pour into a large cocktail shaker.
Add lime juice, orange liqueur, tequila and agave syrup.
On a small plate, combine the sugar and the salt.
Rub rims if 2 rocks or margarita glasses with a lime wedge.
Dip rims into sugar mixture to adhere.
Add a handful of ice cubes to the shaker and shake until very cold.
Fill the sugar rimmed glasses with ice.
Strain the cold margaritas into them and serve.