The reason you don't need to be an expert in all these things is because there are governmentally mandated codes, licensures and bonds with which all such workers must comply or face governmental censure. These standards have supposedly been crafted to represent an acceptable minimum quality of work by qualified persons.

Sure, but you hire professionals to perform and inspect this work, and at the end, have a local official verify the work has been done. Your example really stretches the analogy as buying/renting a structure is not at all similar to trying to get a stranger to build a core product that you can't maintain.

That might be a better analogy, yes.