The investigations have been complicated by elaborate supply chains involving multiple cross-border middlemen.

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Purchase cards from chains with multiple brands like The Gap, which owns Banana Republic, Old Navy and Piperlime.com or Williams Sonoma with its Pottery Barn and West Elm stores.

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All three were provided wine lists from nine steakhouses, most of them chains with multiple U.S. and even some international locations (the exception being New York's Peter Luger, which only has two locations).

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