As an aside, this is the reason i don't instantly berate DIYers, short courses or anything like that. You get corner cutters and bodgers everywhere.
I'll always remember going to a house wired in the 60's by an old boy with no qualifications, just a good base knowledge and plenty of Readers Digest guides. It was his own house and as such, he was invested in making it top quality- and honestly- it belonged in an art gallery. Absolute work of art, even the slip tubing in the garage. Everything was neat as .
Similarly today, I'm about to go and tidy up a connection made by a retired electrician of 45 years who was working maintenance here before he fully retired - choc block connecting some RFC singles together, not encased I'm anything and just lobbed above the suspended ceiling grid.