Knisely's gets their chicks from Ideal Hatchery in Cameron, TX. I like to "play detective" and figure out the hatchery by the breeds they list. First I found Silver Grey Dorkings, a breed no other commercial hatchery offers, but the "clincher" was the "Ideal 236" layer chicks. Of course no other hatchery is going to carry a chick branded to Ideal.
Sometimes the hatchery sends straight run either because they are cheaper, or just a mix-up, but most likely you just got unlucky. The hatcheries promise 90% accuracy, but you have to buy enough to make that statistically viable. 2 out of 5 being cockerels just means that 15 other Doms sold by the store were indeed female, giving them their 90%.
All Black Barred breeds are sexable at a young age based on the amount of white on their wing feathers. Males have twice as much white and stand out in a crowd, but looking at just one or 2 makes the amount of white a lot more subjective. At hatch, all you have to do by are the size of the white headspot and the leg color. Females have smaller spots and darker legs. None of the black barred breeds are as easily sexed as the sexlinked hybrids or the autosexing breeds.