I will admit that intersexing does produce predominantly female seeds, but a female plant that produces male flowers will still produce a few scattered males. To quote Jorge Cervantes:
Some growers intentionally use the pollen from intersex plants to fertilize females. They have found that the seeds and subsequent offspring produced from this union will be predominantly female. The major problem with this technique is that these plants will have intersex tendencies. By selecting parent plants that have intersex tendencies, we ensure that some of the progeny will also have intersex tendencies. Using pollen from an intersex or hermaphrodite plant is an intentional selection for intersexuality-like begets like.
Some seed companies market “feminized seeds” which are produced by collecting pollen from carefully selected, latent, stress-induced hermaphrodites, and use it to pollinate female plants. This process is time consuming and arduous, but yields mostly female plants when grown without stress. However, under the stresses that resulted in the intersexuality for the pollen parent, the progeny will often show some degree of intersexuality as well. Again, like begets like.
-Jorge Cervantes
If you want to create true feminized seeds without the tendencies of intersexuality, you will need to induce male flowers on a flowering female plant using silver thiosulfate. I believe that Robert Bergman has an article on this process in the guides section. I hope this clarifies my statement from earlier and also points out some of the inherent problems of intersexing.