It depends, if looking for advise on how to use excel from someone, I don't think that they need to be certified or whatever.

For asking someone to do some web design or a logo, I don't think it's necessary either, but there is a limit somewhere.

Think about this way, if you yourself or someone in your family would have heart disease, would you take advice from an acupuncturist?

I bet you wouldn't. What are the odds that Kris Kresser without any formal training or experience managed to better understand the science behind such a complex topic like heart disease than full-time scientists and cardiologists?

Self-learning is great for a lot of things, but heart disease is likely not one of them.