At what point is a business making excessive or immoral amounts of profit? Is there a profit margin businesses should be limited to? Why or why not?
I do not see limiting profit margin as the metric to focus on. If someone sells pencils in the street at $1 and it cost them 10 cents each to build inventory, is 90% profit obscene in this case?
What I see as more important is limiting the amount of power and influence money can have politically.
I would also distinguish between essential services such as utilities and non-essential commodities, products, and services. In the latter case, the market should decide with fairness in markets maintained with appropriate regulation.