This is not accurate. You obviously are not familiar with TSA regulations.
It has nothing to do with duty free.
it is international regulations that you cannot take liquids on a flight.
if you buy a bottle in an airport after you pass through security you can take it on board. But if you have a connecting flight , in going from one flight to the other, you have to pass security again, and security in any airport will stop you and confiscate the liquid. This is common knowledge.
The only way you can carry liquids in your hand luggage is by buying in a secure area and going on a direct non stop flight. if you change flights, you have a problem.
"Another option for bringing alcohol in your luggage is to purchase it after you go through airport security at your departing airport. These purchases are still subject to the duty regulations mentioned, but you will be able to place the bottle in your carry-on since you're already through security. Keep in mind though that some airports require you to go through security again after you get through customs, so if you have a connecting flight after you arrive in the U.S., you will have to stash the bottle in your luggage to get back through security. You will have your luggage with you when you go through customs, so you can stash it then.
References
Customs & Border Patrol; Determining Duty; August 2009
Transportation Security Adminstration: Make Your Trip Better Using 3-1-1"
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www.tsa.gov]
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barcann.livejournal.com]