In a single pack of feminized seeds a grower CAN produce:
Females.
Hermaphrodites.
Males.
There is no way to tell a male seed from a female seed. All seeds on the market claiming to be 'all female' or '100% female' are actually feminised seeds.
Feminised seeds are, by definition, NOT 100% female.
This is because they are created using at least one hermaphrodite parent plant. A hermaphrodite is a plant with both male and female reproductive parts, almost always starting out as a female and, later, growing male parts. Therefore, any seed resulting from the union of a female and a hermaphrodite must inherit the hermaphrodite tendency.
In practice, this means that while most or all plants grown from feminised seeds may appear female once flowering has been induced, they may, at any point in their lives, produce male flowers. If this happens near the end of a harvest, it can ruin an entire crop.
With natural seeds, you only have to remove the males at the beginning of the flowering period. With feminised seeds you may have to keep watch for the entire flowering cycle.
Furthermore, since stress is one of the main factors responsible for triggering hermaphrodism, feminised seeds do not make ideal mother-plants. Every time you cut potential clones from a feminised mother, you run the risk of it turning hermaphrodite.
