I recently had a fret level on a brand new neck done for me by a fantastic local guitar tech; it is now the easiest playing neck I have ever owned (SS frets and ebony board certainly help). My question is: upon bringing the uninstalled neck to him, he took a quick look down the neck at an angle and said it would need a fret level. What are techs/luthiers SEEING when they look down a neck and make such a diagnosis? Is it something in the way light is reflecting on the frets, perhaps some unevenness? I am sure the cynical answer is "a big, open wallet" , but I do completely trust this guy, so I am just curious what the tell-tale signs of this are.