Genesis once bubbled...
Sure they can.
If I could get commercial insurance I would rebuild regs for roughly the same prices that the shops charge, and make money doing it.
Not a lot, but money nonetheless. It would be a profitable business, if not a terribly-lucurative one.
Fills would be a bit more expensive, but I could provide fills off my personally-owned compressor for comparable prices to that charged locally, and Nitrox for a bit less than that charged locally, particularly if I banked both air and 40% (to mix anything from 21-40% on demand)
Now training is another matter to some degree. But even there, with the cost of an OW cert hanging around $200 (after taking out the "givebacks" and such, and adding in the cost of materials) in this area, that's $1200 for six students - the usual maximum for a class.
That's about $30/hour, assuming 40 hours of instructional time.
While not a princely sum, its also not chicken-feed.
Now yes, the current structure is different for the instructor, since most of the course fees end up being "eaten" by the shop. But assuming independant instructors, its a fair living wage all the way around.
The LDS as a "gear pusher" at 100%+ markups is not the only way to make a living at this game. Independant instruction can be reasonably profitable - $30/hour isn't bad money by anyone's standard, and neither is $40-60/hour for overhauls.