I guess when people walk into an airport shop looking for headphones, they aren't just window shopping, they absolutely intend to buy a pair because they need it for the flight.

That could quickly change once people get fully accustomed to in-flight wireless: browse the web for a shortlist on the first leg, feign interest at the stopover shop, price-compare and commit on the connecting flight.

The logical consequence would be manufacturer stalls replacing shops in the waiting areas (like a permanent trade fair) and Amazon adding pick-up warehouses to the exits.