Costco’s online gold sales are popular with fans of the bulk-goods retailer and enthusiasts of the yellow metal. Photo: Bing Guan/Bloomberg NewsRon Williams,a retired Air Force production superintendent in Utah, usually buys gold investment coins and bars from his precious-metals dealer. But when he found 1-ounce gold bars available on Costco Wholesale’s website recently, he decided to give them a shot. “They seem pretty competitive with other bullion dealers,” says the 62-year-old Williams. “And the shippi ...