Folks talk about the consistent bevels and what not. What about these knives that were ground unevenly so that the blades face is uneven and as a result youre bevel will never be straight all the way through. What about the blades that are thick? Sure enough you can sharpen the edge well, but is that really all tht matters?
So a good sharpener imho is a guy with enough experience to properly evaluate each blade and being honest with himself about what needs to be done [and not looking at the time spent/money he charges], and looks to the story of the blade.
Does the blade require thinning? Does it require polishing? What about handle? Straightness, steel, purpose, owner, use, quality all make difference, to me. Maybe not in the effort put but result expected.
Just the edge achieved is not even close to being the most important.