I have to agree with both MD and BP on this. I work with weapons for a living and have had several of our shooters come into the armory and I do work of various nature for their weapons then I laser bore sight it in, then take them to the range for target time.
I have sighted in my own weapons since I have been able to and was so instructed by my father growing up. I willnever had someone a weapon and say its dead nuts on for I know its not till THEY paper it. I used to have some BIL's that came to my farm prior to deer season to "Sight their guns in". I got my sand bags out (before lead sled days) on my concrete bench and all they did was use the bench for a table.
They were making scope adjustments from what they saw their impacts were from shooting OFFHAND!!!!!!! No rest, no sticks, nothing. I ask how. Their reply, "well, there are no concrete benches in the timber"!!!! I just walk away and was thankful they were not hunting my land. So over the 40+yrs I have been shooting for recreation and work, I have seen enough to say that the professionals are correct in sight in your own stuff and test it on paper before aloowing it to be claimed as correct.