Buying a used house, the mortgage companies IIRC require a full electrical survey to be carried out before granting any money for the buyer etc. I have done many wiring jobs for homeowners and many industrial ones as well in my working life and I have never come across any sockets that were not correctly wired. All terminals are very clearly labelled as to what they are.
I have never come across outlets wired incorrectly if they were originally done by a sparky. I HAVE come across outlets wired backwards by someone who had no business doing electrical work.
Many years ago, I got bounced on my bum off a ladder from an outlet wired by a sparky.
We were installing CCTV cameras, mounted on pan/tilt heads which were, interestingly, operated by raw mains.
Limits had to be set individually with these, as in some places, they could bash the lens into some hard object, like the wall!
To this end, there were stops which had to be set inside each pan/tilt head.
So we didn't have to run back & forth from the control room, one of the "clever chaps" made up a box with two large key switches, which could be plugged into one of the GPOs conveniently mounted on pillars throughout the building.
We could then, with side of the device open, motor it to the required limit position, then adjust the limit switches.
For some reason, the internal (assumed) Neutral connections to the device were not insulated, & when I adjusted those units with a correctly wired GPO all was well, but when we used the one where the Active & Neutral were reversed, I got a nice shock, & fell off the ladder.
In fairness, if the "clever chap's" box had used double pole switches instead of single pole, or the device I was adjusting wasn't so cramped inside so I was less likely to brush a "hot bit", I would still have been safe.
Instead, everything went the other way, & I landed on my bum!