I have to be honest and say that if a candidate comes to me for a skill test with an attitude, I will play the skill test totally by the book. Cause he's the sort of guy who will complain about the conduct if/when I fail him. If you play the skill test totally by the rules he /she will invariably show good reason to fail. This is not to say a good attitude candidate gets short change and a skill test not played to the rules. But if someone shows good airmanship and a reasonable flying skill, I feel confident they will go on with the licence and learn from their own mistakes. I tend then to give them a second chance at the odd mistake and always try and give them the benefit of the doubt provided they are safe. Something to do with 'Gut feeling?'
If I am teaching a bad attitude student, I shut up let them get on with, wait for them to F... up big style so that they probably S... them selves and nothing else normally has to be said. Let them make the cockup and they sure as hell will realise who is right!!! In fact I will sometimes go to the extent of overloading them or giving them much harder tasks to do, just to catch them out. They have to learn whilst with an instructor because once qualified the could kill em selves. Always let them make the mistake. Don't hand it to them.
The art of a good instructor is one who plays the lesson to the students capability, task in hand, student experience, charactor, and of course their attitude to the whole flying thing.