Well, I don't do Leopard Geckos, but I would think that the same rules apply to Leopards as to Balls.

Males are harder to sell because you only need one male for a harem of females.

Females still need to be of good quality for them to be able to be sold, in my opinion.

Selling in general is going to be a challenge unless you have a setup or a group of people already interested in your animals. It takes time to sell stuff, and if you aren't patient, it may work against you.

Just my two cents.