@iman: all breeders need to be pre-conditioned regardless of their origin. The longer you feed high protein/nutritional foods, the better. Both need to be healthy to successfully breed and survive .... males often stress themselves out and not recover.
Most female fish (incl betta) have two egg sacks and only use one on each spawning. The empty egg sacks is quickly filled specially if they are fed nutritional food. So they always carry eggs.
@1f2f: I'm glad to see you understand that pet store and show fish comes from the same breeder/s - with the difference that pet store betta's are show rejects. The important thing is to know what to look for and how to combine their genetics. To be on the safe side, wait until they are fully grown so they will show if they carry any genetic defects or not.