The only way that breeders know 'For sure' that the hatchlings are definite hets is that one of the parents were homozygous to begin with.

Say someone bred a Lavender albino to a normal. all the babies are 100% hets for lavender albino.

now, someone can breed two of those 100% hets together,some of the babies would be lavender albinos but the others are 66% possible hets. They have a good chance at being an actual het but the fact that you can't tell just by looking at them they would be sold accordingly. They would not be sold as if they are guaranteed hets but they would probably cost more than a simple normal,so yes dealing with hets you could end up with a more expensive normal, thats the gamble of dealing with hets.