I look at makeup artist profiles and I see the things with bright colors and they look impressive, but really how do you find one who is excellent at a classic job? What are the technical hallmarks to look for? If they did the job right the makeup is invisible, right? How do you know what is good makeup and what is not?

Like photographers most professional good artists know when she or he is looking at an ametuers work.  We look at the details in the makeup like a photographer looks at lighting, composition etc.  It's hard to explain to someone not in the field but we can pick out a bad makeup job with just a glance.

There are a few obvious signs like the face not matching the body but there are many clues that give away a novice. Show me a photo and I can pick the makeup a part but have a hard time explaining without example. 

oh forgot to add, sometimes what looks like bad makeup is bad lighting.  I heard a photographer complain once about the dark circles under the models eyes (not on a job I was on but a job he did, he showed me the photos)  I looked at the shots and I could see his lighting was causing it, sometimes there is nothing an artist can do if the photographer doesn't know lighting.