ya, like lit up says, genes is suspect numero uno. nothing you can do about that. once a plant hermies and produces bag seed, and you come by and grow those seeds, the hermie cycle is pretty much locked in place. HOWEVER, you can do plenty to prevent excess seeds from forming. culprit number 2 after genetics is light leaks imo. make sure there are absolutely zero light leaks. plants tending to hermie will put up a fit if there is even the slightest light leaking. heat stress is another biggie. make sure your plants receive adequate ventilation and air circulation. have a fan running while the lights are on and make sure the temps are okay. the key here is STRESS FREE. anything you suspect will cause the plant to stress out, will likely result in more seeds. less stress, less seeds. if you can conquer a plant that is known to hermie, then you can more than easily raise purchased, high quality seeds without having to worry about hermies. growing bag seed is tougher overall than growing purchased seeds.