While it's trivially true that most adults command a basic understanding of design, everyone nonetheless believes that they can do good design work (graphics, audio, architecture, etc.).
If people are used to getting their own way, this overconfidence creates serious errors. These VIPs need to have input into the process, and the Design should be informed by their ideas and the firm's marketing constraints, but the final edit should be controlled by the design lead.
Granted, not every firm has a designer on staff. And even if they do, they may be already over-projected. The Solution? Nominate a design lead and stick to that decision. Usually, you'll be surprised by what they can do.