A good luthier would have shown you exactly what the problem was, in front of you. The luthier that I work with always shows people, no matter how new or experienced, what is wrong, in front of them, and explains what the problem is so that they understand. If there is a fret level required, he can show them the fret unevenness with a ruler or fret rocker. Showing somebody that the nut is bad is just as easy, just by fretting the string and having the buzz disappear.
The difference is that the people in your example above, are just salesmen who may have some knowledge of guitars. Real luthiers take pride in their work, and know that looking after people's guitars properly is going to generate more business in the long run. The people in your example were after the one-time "big score", and didn't care if you came back, or were happy. Real luthiers, whose reputation rides on every guitar and customer that comes in, don't work that way.
To see how a real luthier works, look up the youtube channel twoodfrd. This is a good example of how what I am describing a "real" luthier does things.