I don't mean to be too discouraging, but I think it IS a [nearly] impossible task. I'm under the impression that only the best seamstresses do buttonholes, and making buttonholes is a very specialized task, meaning, once a manufacturer finds a good buttonhole maker, that person only sews buttonholes from then on out. A good handsewn buttonhole, one that will last over repeated use, is very very difficult to master, and is a source of pride for many artisans.
I strongly disagree. This statement is correct ONLY if the word profitable
is inserted. Beyond that, it is entirely incorrect. Virtually anyone with a decent pair of hands and a love for the art can learn to make handmade buttonholes. It will take a bit of practice. Making a jacket's worth of handmade buttonholes (8-16 or so) may take an amateur a couple of days or even more. But it can be done. Maybe we'll even hold a buttonhole seminar at the next Sartorial Excellence. When "those with the professional expertise" are referred to, those of whom are being spoken are people who can accomplish that same task in from 30 minutes to a couple of hours. And, yes: they are like gold and are usually hired for life.