Costco returns many items with a full refund, and it's not always necessary to have the receipt or original packaging of an item, but rules can vary when it comes to alcohol.
Per its return policy, Costco doesn't allow alcohol returns "where prohibited by law.” All states have distinct rules for returning alcohol that dictate how Costco handles returns.
For instance, while residents of Maine can return alcohol with a receipt within 10 days, California residents can only return alcohol if there's an issue with it, such as spoilage.