Here's my hard and fast rules for wearing reps, and for pulling it off convincingly.
Avoiding the "Is that real" question
1. People "size you up" when meeting you. The quality of your shoes, wedding band, and glasses (if worn) all should be on par with the quality of your watch. If not, then it's more likely to be suspect.
2. Wear decent clothes, and get sizes that actually fit you - the baggy sloppy look just makes your nice watch look way out of place
Most of the other traditional "rules" of dress don't really apply anymore in today's world, but these 2 tips should hold you in good stead and make the wearing of a $5k or $10k watch a lot more congruent with your overall appearance.
Dealing with the "Is that real" question
1. Decide way in advance, whether you are going to be truthful to this question or not. There is no halfway answer that is convincing and any hemming and hawing will be a dead giveaway.
2. If you decide to be truthful, say something like "Of COURSE this isn't real, there's NO WAY I'd pay $10k for a friggin watch".
3. If you decide to not be truthful, say simply "Of course it's real" and look at them like you are mildly annoyed. No further comment or explanation will be necessary.
Whichever approach you decide is right for you, remember to be firm and decisive and fully committed to it. Any waffling and you're done for. Wear it with confidence.