How long have you been doing it? I found upper class to be largely the worst tippers, underclass, which, come on, would usually give me a buck at least. Upper class would stiff me with no internal issue more frequently than anyone. I have delivered 70 pizzas and pounds of salad and been stiffed. But I've also delivered 90 and tipped 150, it's a crap shoot with the upper crust. I think the preference can be that the over tipping can make up for the 40% rate of zero.