I live in the USA (NYC), so I would not be purchasing liquor in the USA to bring to Europe. I've also priced duty free stuff at JFK...not much better than duty free in Europe.
From reading items on the internet, I think Amsterdam and Shannon are the cheapest duty free shops in Europe--I rarely depart from either.
Does anyone know if duty free is pre or post US CBP pre clearance in Shannon? Also do the Shannon duty free shops provide the tamper proof bags?