Yes I have and so does everyone. This happens all the time in life. You trust professionals when you don’t have the knowledge, experience, or ability to physically see something. You trust the mechanic when he says parts under your hood need replacing. Doctors when they give you a diagnosis etc
Sealed grading also implies your trusting the grading company. How do you know that the contents are inside and that it wasn’t a fake resealed box?
Your argument main argument seems to be that they are human and make mistakes. That’s true but they don’t make mistakes often enough to completely throw out their judgement and expertise.
Regardless of my input or your opinion, the fact is the market currently disagrees with you and has for a long time. Comic book grading where you can’t see the inside page condition or artwork has long been successful. Sealed grading and cib grading have taken off so much so that the market is large enough for 2 main players, one of which has so many orders currently they had to put a hold on taking in further revenue to satisfy the demand.