I'm not a quilt judge, but a quilt judge on another forum said:
"It is about 40% judge preference and 60% merit. But the judging results should be based on a lot of things. The biggest question is how well the components of the quilt are done. If that quilt is a basic pattern and is pieced beautifully, that should sit well with the judge. If the quilting design is a basic design and done exquisite, that should sit well with the judge also. But on the flip side, if there is an extremely difficult piecing design and it's done "not so hot", that judge should recognize that fact. The same thing with the quilting and the binding. If the quilting has a very detailed design and it is "not so hot", it should reflect in the judges scores.
Another thing the judge should look for is how the block pattern, the color choices and the quilting design relate to each other. I.E. A simple 9-Patch most of the time doesn't need to be completely covered in feather wreaths. And if the color choices are dynamic or subtle, the judge shouldn't let her "preferences" show in her choices. This is where the judge should put her "preferences" aside and judge the quilt on the quilter's choices. I.E. If you are the judge and lime green isn't your favorite color, he/she shouldn't penalize that quilt because they don't like green. As the same on the flip side: if Civil War blue is their favorite color, they shouldn't give that quilt preferential treatment. The quilter's designs should stand on their own and if all the quilting overtakes the block pattern and color selection, that will detract from the completed quilt.
In a nutshell and with a fair judge, the better the execution of the quilt and "reflecting" (not the main factor) on the degree of difficulty, the higher the judge should rank the quilt."
After being a scribe for a judge, I know she looked at the backs to make sure there were no tucks or pleats quilted into the quilt and she was very picky about the binding being full and even - she really hated the backing being folded over as a binding and machine stitching the bindings on both sides.
Hope that helps.