I'm skeptical of this. When a sink is clogged, the toilet won't flush, or a light switch doesn't work, there are only a handful of potential causes, all of which are well known and can be remedied after watching a Youtube video. When electronics fail, there could be a million reasons why. Most people are better off buying a new device and getting a warranty on it.
You know what's usually useful? A youtube video of disassembly, digging up a service manual with google's help; pretty much the same as a toilet, but generally far safer than trying to fix a light switch.
Once upon a time in the age before I dedicated my life to all things software repairing color tvs was one my sources of income. I respectfully disagree with your assertion, electronics can fail in very many different ways. All the way from 'rodent electrocuted in HV power supply' to passive component that never fails somehow in fact did fail.
Even something as mundane as a coil-over-a-resistor can fail if the conditions are right. And don't get me started on bad soldering connections, corroded connectors and a million other little details that can affect the functioning of a device to the point where the repairguy gets called.
This was before the days when oscilloscopes were portable, and unfortunately also before the days when I had a driving license. A typical house call would end up with a working TV or VCR and me learning yet another way in which things could fail.
Main tools: a couple of folders of schematics of the most commonly encountered models of TV/VCR (pick the right one before you leave, hope the user read the type plate correctly), a stack of matchboxes with passive components, some of the more common active components with enough spread that you could cover most cases, a soldering iron and a very large collection of parts scavenged from old TVs waiting for the opportunity to recycle them.
The cost is not on the component, but the knowledge to know which component to fix. That's not something that come cheap.
Yes, but 990,000 of them would be capacitors. Check capacity and ESR, replace bad ones - done.
Consumer electronics are very reliable, if the product lives through the warranty period, it's likely to last for years. Which leaves a small window of opportunity to service expensive and relatively new, but out of warranty products, and many repairs will be impossible or prohibitively expensive. It's not like the old days where a few drawers of spare parts could fix most problems, now much of the functionality for most products is embedded in a control board that's not available as a replacement, you have to scavenge it from another product (and hope that the hardware rev is compatible with yours).
So yeah, you can fix some things with discrete components, but you're pretty much limited to expensive products - you likely can't fix a $49 blu-ray player at a price you can make a living from.