Like you stated, wiring isn't rocket science, but then many other things aren't rocket science either.
The part about "known good earth ground" got snipped.
***When wiring anything that's line powered.. a replacement receptacle or a major piece of equipment, the first connection I make is to a known good earth ground.***
He may or may not be an intelligent electrician, but he's had his children and wife living in that house. So who is responsible for confirming that the electrical system is safe? Realtor, gubmint, seller, inspector, non-existent contractor etc.
The thing is, none of those other people sleep in that house, and they'll all just point their fingers at each other, eventually assigning blame to who ever makes the best scapegoat. The other people's responsibility most likely ended with the sale of the house.. and that leaves only one other person.
The responsibility ends up being the homeowner's.
I think the majority of home fires are determined to have been caused by "faulty wiring". There hasn't been a lot of wire being sold that doesn't meet specifications. Realistically, many home fires are caused by improper installations or misused circuits and/or misused electrical equipment.
A person can buy or find free information WRT safe, proper wiring practices, so there aren't many reasons why wiring should be done improperly, but one reason is arrogance (which is essentially choosing to be ignorant).
I've seen a lot of horrible electrical work.. including a spliced & taped romex junction (no wire nuts with a branch meeting a run, adding 12 to 14ga) hanging free inside a wall without a box.
People are stupid, but add tighter-than-a-frog's-ass cheap to stupid, and they'll perform feats that are difficult to imagine, by anyone with the slightest amount of common sense (which needs to be renamed uncommon sense, as it seems to be fairly scarce nowadays).