Hehe, fish love live food. If you're not trying to breed and are worried about over population, forget it. The betta and the mommies will eat the fry.
Uh, yum.
If you're planning to breed, you probably need another tank. (That's how I ended up with 3 tanks, hehe)
The only way that bettas would have fry is if both the female and male were together and then separated after the eggs were laid. The female would try to eat the eggs and either succeed because the male's a weekie or die because the male defended the eggs and killed her.
So, that's kind of a weird excuse for not selling bettas imo.