Once while eating at Restaraunt outside I noticed a clear plastic bag filled with water hanging in the doorway and asked what it was for. They told me the water in the plastic bag refracts the sunlight and hurts the flies eyes and keeps them from going inside. It seemed to be working real well. Maybe give that a try also. Just something to ponder. [" it was a dark liquid spray that he used" ] could it have been liquid smoke?