So, how would we go about defining policies that prevent “excessive” profits while still allowing for building buffers in risky and capex heavy industry?

More heavily tax profit above a certain level? Allows for funnelling back some of the excessive profits. Suffers from the same tax evasion as we currently have where profits are skewed on the books with all kinds of accounting tricks.

Demanding sales prices cannot exceed cost + 10% of cost? In aggregate or per unit?