Yeah, it all does seem a bit ad hoc.It's all a bit confusing. When I last had my Napit assessment they were very thorough. in fact, before that when it was Stroma, they were also thorough but Napit were very thorough. It does sound like they are not interested in complaints though.
I can't understand why they act professionally when it comes to yearly assessments, but not so with complaints regarding shoddy work.
If this is your home and you are still concerned about the safety of it, I would continue asking questions on here until you feel you have more knowledge about what exactly is wrong with the house (backed up by regulations) and then take it to UKAS (or whatever the body was that was mentioned in an earlier post). Frustrating for you though and I hope you get to a position where you are happy with the house.
My guess is that if the scheme bodies make the assessments more stringent and the electricians have to be more thorough to pass, then in general they probably feel that the vast majority are going to stay compliant throughout their jobs. Obviously there will always be those that scam the scams and offer up examples that they have either had someone else do, or actually spent the time and effort to get the odd installation right just for assessment purposes, with no regard to any other work they produce there after.
This shouldn't however excuse the scams (schemes) from following up complaints and doing something about any dodgy members that are ruining the reputation of the genuine trades people and also the scam itself!