Hmmm... there must be some magic here that I just don't see.
There is no real magic. There is "no real magic" in a good craftsman making furniture, a good mechanic fixing a car others have been failing, is also no magic. Just humans who know their job better and have more skills, more dedication, more interest, more drive, more ....... than others.
One or other way everybody can string when they have a machine. And one or other way it is not allowed to state someone just cannot do it that well.
But who at a pro shop/club is actually stringing the customers racquet and how long have they been at the job?
There are many average craftsman doing a decent job. But many pro shops are done as an extra to coaching, as a service, making some extra bugs or what ever other choices. And you are right many shops just have somebody do the stringing.
Stringing is a manual job, fingers, feeling, having bad and good days.
Let me give an example of a quality stringer: He can do 9 the same rackets and strings in a row within 3 hours and string 3 at 24, 3 at 24.5 and 3 at 25 kg. And all sets of 3 rackets will sound the same. And the tighter ones will sound just a bit higher in tone.
So just test yourself. If you have 3 of the same rackets, put the same string in all of them at the same tension and test if you are done if the result is the same. And that is the only the first most easy test the result.
If the recipe is correctly put together in the first place and followed to the letter with the exact ingredients, different results should not be expected.
There is outside temperature, changes in quality of ingredients, humility of the day, air pressure of the day, all factors not in the recipe. But a quality craftsman just knows how to deal with. Why is a croissant in France so much better than in the states? And as to be expected you have better bakers than others.
assembling Ikea furniture after putting in a reasonable effort is probably below the lowest common denominator.
Not every one is as handy. Not every one can sing. Some think they can but all those X-factor America got Talent do show many who are not really appreciated and they can sing so nice......
The lawn at Wimbledon has nothing to do
Wimbledon is the end result of some water, some grass and some machines.
All I am saying stringing is not as easy as it looks. It is no rocket science. It is craftsman's job.
Peter