Tiffany said it found out about the marketing through a customer who said “that she was disappointed to observe that Costco was offering for sale what were promoted on in-store signs as Tiffany diamond engagement rings,” Somaiya reported.
Tiffany said in the lawsuit that it would never sell rings at Costco.
Even though Costco stopped branding the rings as Tiffany, the damage is done, according to the lawsuit.
"As a result, the suit says, there are 'hundreds if not thousands of people who mistakenly believe they purchased and own a Tiffany engagement ring from Costco,'" the Times reported.
In addition to all profits made from selling the rings, Tiffany is asking for damages that "take into account the value of the Tiffany brand in bolstering Costco's business," the Times reported.
Costco told the Times it had no comment, which is standard for pending litigation.
Costco has recently pushed to work with luxury brands.
It's offered merchandise from 7 For All Mankind, Tumi Luggage, and Betsey Johnson.
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