Here in Norway, the owners of such shops have always been "asset rich", because they pretty much own every asset in their company. That means vehicles, tools, shop, parts and products inventory, and what have you.
Prior to enrolling college, I was an (electrician) apprentice. I ditched that for a degree in electrical engineering. During college I took on a variety of part time jobs to support myself - a bunch of them were temp trade jobs. Roofing, construction, and what have you.
I'll tell you this though: I've never, ever met a shop owner that didn't work from 7 in the morning to 9 in the evening, minimum 6 days a week.
Some of these guys practically grew up in their fathers shop, and have been ingrained with such a hardcore work ethic, that work is all they know. They could liquidate or sell their shop, and retire - but I've yet to meet anyone that does that. I've seen more shop owners die before they retire, due to the lifestyle choices around this kind of work. And those that "retire" will anyway keep hanging around the shop.
This usually leads to what we just called "voluntary involuntary" overtime. Basically the shop owners will assume that everyone loves work as much as them, and will assume everyone wants to work overtime 6 hours a day.