This is a quick guide on how you should handle rule questions in a tournament setting. There are plenty of times you may question the validity of a rule or how someone views something. Minor stuff that won't change the game don't bother. You don't want to cut into your game time. But if it is a big rules question or a game changer never assume your opponent is correct if you have any doubts. If you don't question rules you may miss out on an opportunity. In a non regulated game like 40k each player has to be their own judge. Everyone gets rules wrong from time to time especially if they don't play as frequently. Take your time and go ahead and look it up. There have been plenty of times I have been wrong or questioned my opponents and they were right. But the same goes the other way. I have saved major losses via questioning rules and getting the proper answer.
There may be some people who really enjoy to flaunt knowledge and try to tell you that a rule is whatever way they say it. Never let your opponent dictate to you what is real if you question it in your head. The only one you can blame is yourself for not looking that rule up. You will regret it if you lost a game for it. Tell your opponent you will look it up and take the time to prove him wrong or if he is right just continue on. If your opponent just wants to continue the game tell him to show you where the rule is that is in question. Some of my most heated games of late end up having rules questions and I never regret taking the time to play the game right. If I find out later that something went wrong that I played and it was my miss interpretation of the rules then I do feel bad and I learn from the mistake and wish my opponent had stopped me so we could have fixed it then. In the end remember it is a hobby and a game and don't take anything said or done personally.