most sites with "quality control" are biased in the one or other direction. On some sites they show the tenthmillionst render of an Audi on some sort of gradient background, but if you send a landscape render, or a render of a plant, then this is not original enough, not what they are looking for, whatever.
Don´t care about it. In some cases they have some valid points, but overall I think it´s much easier to push a car render through ;-)