Really knowing how items look in relation to one another and knowing how and where to draw the eye is a clear sign of an expert.
Contrast in design seems like a simple thing but in he real world its one of the most difficult things to pull off without creating clutter. If you know how to create proper contrast then you have most likely been a decorator for a while.
A home is art you can live in. Creating something beautiful is one thing, creating something beautiful and truly functional requires another layer of thinking
Knowing the size of objects and where to place them to create a certain affect or feeling is really an advanced technique and when done properly can set your designs apart.
Glamour is hard because it is always on the border of outdated or cheap looking. but if you can use sleek materials and vintage peaces with bold fabrics and really create something that is not cheap or outdated in 3 years then you really know what your doing.