I think examples of what you're looking for would be much appreciated

A nod in the direction you wish to take would help all the designers working on your project to get what you want. That, or a more constructive brief in the first place.

I would also like to point out that for you to give a rating of 1 star for my submissions - I take as an insult. I think you are confusing Quality - (which is part of what the rating system is for) - with your personal aesthetic tastes which is a different thing altogether.
I do not submit 1-star work. I have been creating book covers for years, and have seen some terrible covers win competitions and some excellent covers win on designcrowd, it is all in the eye of the beholder. Quality is a different matter. e.g. You may not like Porsche styling, but the quality is still there.
If you do not know how to rate a piece. don't bother, as this affects the designer's ratings for their standing on Designcrowd. Long after your book has been published, the effect of your ratings will remain on designcrowd, and other authors seeking 4 or 5 star designers may get the wrong impression.