For starters, just because the watch is duty free doesn’t mean it’s “free.” The stores aren’t running a charity program here.
They need to make their money somewhere, and that can often come from oh-so-slightly hiking up the prices, so that watches might actually cost a little bit more inside airports than they do in stores elsewhere.
Indeed, a 2018 article in The Telegraph noted that more than half of consumers think they can find a better price for luxury items on the high street in London, Paris, New York, or elsewhere than in an airport terminal.
They know that airport shops might subtly hike their prices to compensate for the duty-free nature of their products, and would rather just buy them at their destination or back home.
That isn’t even getting into the horror stories of when duty free turns out not to actually be duty free.
Customs agents are extremely picky about what does and doesn’t count as duty free.
The slightest bit of extra ornamentation may cause you at the very least a headache and longer wait in line, and at worst a duty charge, making that supposedly “less expensive” watch which might have already cost more than if you bought it outside the airport now cost even more.
This isn’t to say that you can’t buy a nice watch at the airport, or that there are no great deals out there.
At the same time, if it sounds too good to be true, it probably is.