You are sure what is fine?
You are sure that if you find a bottle of whiskey in your garage that you can spill it down the drain, and that you are not stealing from the goy? (whiskey is chametz gamur, right?)
You are sure that your shtar writes out anything which is chametz gamur? What makes you sure of that? My shtar doesn’t. And my rabbi sells chometz both for people who are selling real chometz, and also for people who are not selling real chometz. And has never asked me whether I wanted him to sell all chometz or only non chometz gamur.