I would just like to toss in my perspective about "questioning" the work of any contractor. Contractors, inspectors, and doctors are all of variable quality. They also share the characteristic that they do not have to live with their results. You, as an individual, may know you are good. The people who hire contractors hope this is true, but they really can't be sure.
I do not believe it is reasonable to chastise an owner for questioning what is being done to his home. Even if you are coming from a place where you yourself provide excellent service, you can not generalize your performance to the rest of the world. A "trust the system " approach can yield excellent results, destroy your property, or something in between. If a person is researching something so they can understand what a person they have hired is doing, he should be applauded and assisted for taking the ultimate responsibility. And avoiding potentially destructive repairs.
I have just finished building a house. Even with recommendations and checking with prior customers, there was a huge variance of honesty and competence. One general contractor stole thousands of dollars by pocketing materials payments (yeah, I know - I paid directly for all subsequent materials, but paying the general is normal here). Plumbing was a mess. The foundation had one wall off by 8 feet (my wife spotted it the day before the pour). The sub-foundation drainage was completely incorrect (and some drains left unconnected before concrete pour). It went on and on. I started out trusting the people whose job it was to do these things and not hovering at the site. I wound up acting as the general. Even with the things I could not fix when I found out about them, if I had not validated the work performed I would have a house with many things done incorrectly. Contractor quality and reliability are issues throughout just about any industry. In my career I have had all types of technical contractors with the same spectrum of results.
Simply being a licensed contractor or "being in business" does not automatically require a god-like trust from the customer.
Many things are not found by an inspector. Either because it is something they don't need to inspect or because the inspector is a political appointee who previously sold womens shoes. Reading lots of construction oriented web forums for years, the horror stories about workers and inspectors are common. Ultimately the responsibility is in the hands of the person buying the services. An owner would, in my opinion, be insane not to observe and question things they don't understand or disapprove.
I threw in doctors above as an example of a class of contractors where many of them expect unquestioned delivery of contracted services. I question doctors. I have a right to know what is being done and I always research the drug or process before hand. Even doing this, harm occurs. I identified a drug to which I was allergic. Doctor, because his was bigger than mine, used it anyway. I now have a permanent problem that impacts my quality of life. Two types of cancer not detected in a timely manner despite annual physicals and reported symptoms. They are human and variable. Again; the customer/patient is ultimately responsible for insuring, as much as possible, correct results.