I was reviewing another photographer's work this week - many of us do that so that we become better photographers. It creates some camaraderie and develops creative abilities too.
Looking at photography to determine the quality of the work has many aspects. Lighting needs to reflect and highlight the subject. Eyes need to both be sharp and in focus and in a close up portrait even within the eye-socket. Skin should be smooth and flawless but not plastic looking. Of course these are basic rules and they are made to be broken too.
Then there is styling. Some photographers think that they just record the person or event as it appears. In a boudoir session my friend did, the subject had on an outdated fashion piece (pantyhose) that was not appropriate to the image - the toes and panty were showing. It detracted from the shots that were well lit. The background materials were all wrinkled and patterns clashed. Colors just didn't agree. The red lipstick and wine colored background in some of his portraits were off color.
When I was first learning about photography one of my teachers said everything in your image is your responsibility. In one of my early studio attempts, I learned that hairspray and loose hairs were mine to fix - the highlights will show them in every photo. Jewelery - clasps need to be in the back and earrings level, pendants must hang right where they're intended. Glasses - the bane of portrait photographers - must be angled just so or there will be a big light reflection in them masking the eyes. Clothes need to be straight - no wrinkles, patterns must be of certain sizes not to moire in the images. Makeup should match everything color wise and not be smeared. Too dark under eyes will end up looking like black eyes or age the subject.
All of this detail checking and much more make the final images pop. They make the subject the focus and they make you look good. Isn't that what you expect from your Professional Photographer? It's all the details that you don't see...but I look for in my images.