His customers may pay his bills but why go to a pizza place if you're not ordering pizza or wanting salad? If your car needs a new battery would you go to a shoemaker?
Ahh,a car battery and shoes,2 very different things though.I do see your point though.
That said,If I went to a shoemaker,bought only shoe laces,not a more expensive new pair of shoes,and he threw me out,that would be hilarious as well.What if I go to the gas station,buy a bottle of soda or cigs,and the owner throws me out for not buying any gas?
We could go on all day with silly examples.
Now with food,If a pizza maker also sells salads,a food item,on the MENU,whats the problem?Why sell a salad if you're gonna cry about it being the only sale?
That said,if I had a shoemaker,and he sold salads on the side for profit,I don't think I would order one from him either.Shoe Salad of the day,doesn't sound appealing.