I have ZERO problem with Cajun fiddlers and Cajun made fiddles.
But a professional, production, mass produced accordion shop has the skill, the tools and the option of doing a miter. No miter, no sale.
In another life I was a rare and exotic and instrument grade hardwood broker.. self employed.
My main market were violin and bow makers. I know a bit about the instrument. My wife is a violin player. First chair/concert master at one time.
She has a LANINI hand made violin. She has upscale bows. She played well. She no longer plays which is a pity.
Fun, honest instruments can be made out of simple materials with simple tools and the result can give great pleasure to the builder the player and the listener.
No excuse for a butt jointed accordeon when mitered cornered, better quality (IMO) can be had for the same, or less, money.