There is a difference between not knowing something and knowing it but covering it up to hide something for a deceitful purpose.
There are some few individuals who teach singing who have a very skewed view of themselves. They have managed to ingratiate themselves to the right people by “playing their cards well”. To medical doctors, to those in important positions in voice science and medicine, they are very deferential, making sure to say just the right things. To their colleagues they are disdainful and condescending, making sure to drop names and act “important”.
These people manage to convince others that they “know something” and, in fact, often have very valid credentials. They wear expensive clothing and jewelry, they live in the best buildings. When it comes to promoting themselves, they have absolutely no shame, and will do whatever it takes to make themselves sound impressive. Here in New York and in other places of the USA I personally know of several singing teachers whose regard for their own ability is far beyond what it deserves to be.
I am not impressed by status, money, position, possessions or documents. I rate people based entirely on how they behave, how they conduct themselves in life, and how others regard them. I look for honesty, decency, humility, willingness to work hard, willingness to acknowledge others, willingness to lend a helping hand, unselfishness, generosity, and kindness. In terms of teaching singing, I value first: do you sing well? I value: do you sing well in several styles? I value: do you understand the process of singing as a physical skill? I value: do you work with all kinds of students? I value: do you treat all your students with respect and dignity? I value: can you be honest kindly?
The worst thing in the world is to be impressed with yourself. It is the first step on the path to your own downfall.  If you have to impress someone with what you know, or who you are, be very careful. Actions speak louder than words. It matters not who you are, it matters what you leave behind that helps the world. If you teach, what matters is what you’ve taught and how you’ve taught it. Be a vehicle. You will someday be forgotten but what you give, lives on and on.