Commercial sexing methods, even when done perfectly, have about a 90% success rate. That means if you order 10 females, each chick has a 90% chance of being female. You could get 0 roosters, 1, 2, 3, even get incredibly unlucky and get half or more males. Statistically it would be possible to get 10 males, even with that 90% chance of female.
The only sexing methods that are 100% guaranteed are the genetic ones. Sex link chickens are hybrids between two breeds, which produce chicks that can be easily sexed at birth. For example, male red sex links are white at birth, females are sort of orangey-red. If you cross a sex link with another sex link, the resulting chicks are NOT sex links.
Auto sexing breeds are the same idea, but it's a breed. Cross one auto sexing chicken with another, and the chick sare all auto sexing.