I can ruin your barbacue with some pictures of what I found at a big name restaurant. When the cooks leave for the night the you know what come out to play. Kind of like a bop the mole game through the plastic.
Michigan Exhaust Cleaning
Your First Step in Restaurant Duct Fire Prevention
I used to lease grease filters to one of the most popular Chinese restaurants in my area. My in-laws LOVED it.
Not only was it filthy, but they had about 200 cats that lived in a separate old house in back of the restaurant and always had several 50 lb bags of cat food on the back porch of the restaurant.