>a lot of financial incentive to buying items abroad and importing in your luggage

>very few exceptions

You've got it backwards. If you're an American you're probably traveling through freeports or low tax regimes like Singapore, UK, etc. and don't realise how regressive most regimes are. In places like Hungary, Angola, SEA -- where tax can be in the range of 30-50% you will be lucky not to be shaken down by a customs agent before leaving the luggage carousel.