I private messaged the seller. This is what she wrote back to me: Ours are all pure and we have perfectly good black genes, but there is no guarantee of any gene flaws that show up in birds, that is impossible and it does happen. Most of the time all white feathers in this species disappear after the first few juvenile moltings. We see this from time to time as do all breeders it is just most breeders will kill(cull) any birds that show this trait and we do not kill anything that is born because of a white feather that will most likely go away.
She made no notice of feathered legs. There is no way these are pure... is it time to write the review now or let it go. I don't want anything from her, I just don't think she should be advertising them as "pure" and they obviously are not.
I raise Crevecoeurs, which are all black, bearded, and have no feathers on their legs or feet. Although I have been selecting my flock for over twenty years, I still occasionally get adult birds with white feathers, no beards, and even an occasional feathered leg or foot.
Raising good birds is not an exact science. Many genes are hidden or not expressed. Maybe someday we will be at the point where we clone the perfect bird, but until then, there will be some variation.
Please be aware, too, that you don't know what you are looking at until you are looking at a two year old bird. Like cats, chickens can breed when they are six months old, but they don't reach full mature size, coloring, behavior, until they are at least two years old. Serious breeders look at the whole animal, including health, and they wait to see the mature result, before they select their breeders.
That said, most people who produce birds are raisers, not breeders. Raisers may make some selections, but in my experience it's mostly around looks, and probably at an age too early to tell the final mature plumage and body type.
I am not saying that you shouldn't complain. But I am suggesting that a serious breeder would wait two years, and a raiser would wait six months. Until then it may not be appropriate to build up a lot of indignation before commenting. But it still may be appropriate to suggest that the birds don't look as expected for their age. Perhaps a reference to Feathersite's photo page for Ayam Cemani will bolster your case:
http://www.feathersite.com/Poultry/CGA/Cemani/BRKCemani.html#CemaniChik