I've seen a fair bit of amateur wiring, and I can assure you that most people are not capable of safely wiring up a house.
Isn't this slashdot? Don't we assume that regulars here arw capable of learning this?
In any case, without certification the electricity company won't let you connect to the grid, so you are reliant on what you can produce.
Not only is that not a big problem any more, but all a contractor has to do is sign his name to a piece of paper and you're allowed to connect to the grid. And all he has to do before he does that is look over some of what you've done and see that you know what you're doing.
Not long after I moved into this rental I live in now, I corrected a neutral fault to ground, probably created by a prior resident. So yeah, people can screw up badly. But they can also fix things, and get it right. I put in a branch 220 circuit in my last house, and I did it correctly down to wire gauges.