Thanks all.
I guess if I lived in NC, I would do my whisky-buying (and "spiritous liquor" buying) on interstate or foreign trips at duty free then!
These days it's easy to check prices and compare by volume.
My most frequent trip outside the EU is ABZ-SVG and although Norwegian DF prices are often more expensive than UK duty-paid prices, one can spot the odd bargain when returning - or take a bottle from UK DF on the way to Norway, then pack it in checked luggage for the return. Often I snap a few photos while passing though the inward duty free then check prices online at my leisure later
Glenfarclas 105 was one of those rare bargains at SVG duty-free , which is how I acquired a taste for it.