Nooooothe hatchery has a 98% rate of being correct. Please tell me I can't be that unlucky.
Oh, honey! You should have seen me summer before last when I was dealing with a tiny order from My Pet Chicken. I painstakingly researched breeds that can be auto sexed upon hatch. That means the boys look entirely different from the girls. I ordered six pullets. Two turned out to be cockerels. MPC offered me pullet replacements for the two "mistakes", and I ordered one extra pullet since I needed three chicks to meet the minimum for shipping. Guess what! They screwed up again! One was a cockerel!
MPC refused right up to the point when I reported the youngster was crowing and mating his brooder mates to believe they had made a mistake again. But when I provided close ups of his saddle and hackle feathers, they conceded and refunded my money. But that summer, I had to deal with three cockerels and all the related stress. I was very unhappy with MPC. Still am.
So, yes they make mistakes, and their ability to sex chicks and be accurate is only as good as the aptitude and training of the staff they hire. If you think that chicks where the males and females look entirely different would insure no mistakes, think again.