There really is no way of knowing by looking at someone. The way I can personally tell is by engaging different people with different topics and start mentioning things like 'new light' and arrangements that seem odd, etc. and then ask for their opinion. Of course if the person you are talking to is a die-hard JW they may turn you in but if they respect you enough to keep the convo to themselves then go ahead and give it a whirl.
I've never encountered someone who directly said something contrary to the newest teachings or arrangements. But I know of some brothers by having talked with them that they have reservations regarding certain arrangements and teachings.