Gotta admit HFD I agree with your start post.
If my chap has passed with flying colours I tend to use the opportunity to throw in some possible words and themes of sound advice. As generally you have their attention. If a doubtful pass, I shut up but still give the odd helpful prod. But still play by the rules. If a definate cocked up test and I have made up my mind during that test, I use the rest of the test as a lesson to give the guy/girl a positive building block to learn from before they go off and do their recommended retraining then retest.