rhacoboy is right, it's best not to breed them if you only want to sell. It's a lot of hard work.
It normally depends where you live, but a lot of people just introduce their geckos in the early spring, when the weather naturally gets warmer. So they start their cooling season once the temperature just automatically drops anyway. (Mid or early fall, normally) so they can fatten up their groups.
Actually, it's a billion times better to wait for the females to weigh 35 grams, at least, before you breed. Breeding at 30 grams has too much of a risk of the females becoming eggbound, getting kinked tails, or having calcium crashes. Some people even say that 40 grams is best. Otherwise you can garantee that your female will get a kinked tail, that sometimes takes almost a year to completely heal. (and no, having the tail dropped wont benefit them at all. because then the females will start giving the eggs calcium directly from her body and bones instead of mainly her tail)
And the breeder females I've seen at 40 grams look much healthier than the ones bred at 30 or even 35 grams. And when potential buyers see that the breeders are nice and healthy, they're much more likely to buy.
