All you can do is do all your checks and then classify it as it is. Try not to go over as most HA's have people who will check over everything to make sure they are being carried out correctly and definatley dont go under. But there is always ways around that though (As in if I want to fail something I will find a way to fail it) The good thing about HA work is they cannot leave it and even the NCS will get done (eventually) or at least it is with the HA I do work for.
You will come across loads of bad installs I came across a flue today wasnt sure if it was vertical or horizontal it had a vertical flue kit on it but came out at 45deg through the roof no signs of damage, spillage and clipped so NCS it should of taken a photo but was too busy laughing to myself.