I have come across this many times..."If I sacked all the rubbish workmen, I'd have nobody to build houses"...but these houses are not cheap! No, they are very overpriced, but built cheaply to maximise profit.
That pic of the wiring is just an example of awful workmanship. I'm not an electrician but I'd be ashamed of myself if I wired stuff like that. OK< some of my stuff might be less than perfect, but I'd be happy for someone to take off some faceplates and try to find real fault. It's not really rocket-science to wire a socket, but it's a proper skill to do it properly, and if you can't do it, don't pretend that you can (and charge good money for shoddy work).
To the OP, if your house is covered by the NHBC scheme you could try a complaint to them...but it's a waste of time.