Nobody can overturn an examiners decision regarding fault assessment. Yes examiners make mistakes but to mark a serious fault they have to be 100% certain. Name 1 human that has never made a mistake? You can’t begin to imagine the amount of training they go through before conducting a LGV test.
Usually years of experience either as a trainer or car examiner. Occasionally a free retest may be offered if something very unusual happens but it’s rare.
Finally it’s not about colleagues sticking together it’s about the reality of what happens on test. Test centre managers take complaints very seriously but most complaints are unfounded. Ask most experienced trainers