$320 in my case, despite following all of the rules.
Sorry about your $320, but you were the victim of the complete mess surrounding carrying duty-free liquids around the planet.
It's extremely difficult to get hold of reliable data as to what is and isn't allowed, and even official websites give erroneous and/or misleading information. My
understanding of the situation when flying directly to the US is that duty-free liquids must be delivered directly to the jetbridge (after gate security) or not at all. The TSA
website says, however,
On nonstop flights bound for the US, passengers carrying duty-free liquids purchased at an international airport will not have any problems.
In part, this is because the regulations are now massively fragmented & changing too frequently for web editorial staff to adequately keep sites up-to-date. Duty-free shop staff are (a.) commission-orientated; & (b.) not easy to keep trained with all the latest rules, especially wrt. distant destinations.
Overall, be careful about the rules, and especially so when flying long-haul. Plenty of people have had similar experiences to yours, and not just into the US. The EU rules are also quite complex, and it's very easy to find yourself at the wrong end of them, and losing significant sums of money as a result. Generally speaking, buying duty-free liquids onboard your last flight before your final destination will be problem-free. Anything else and you could have issues unless you
really know the rules.