Web retailer Union Diamond Corp. has closed its biggest sale ever, selling a 6-carat, pear-shaped diamond solitaire ring to a customer in Singapore for $390,000. The woman, who had ordered more than $800,000 in jewelry from Union Diamond in the past three years, becomes the retailer’s first million-dollar customer.

The sale attests to the company’s integrity and customer service, says Scott Anderson, president and CEO. “We’ve been very conscious since day one that our brand and our reputation are more important than anything,” he says.

In order to boost buyer confidence, every purchase includes a $50,000 surety bond to protect buyers against fraud on the part of the retailer or its employees, Anderson says. Visitors to the site can mix and match diamonds and settings, and see how each piece of jewelry would look with stones of varying shapes.

While international sales are growing, Anderson says they still make up only 3% of sales. He says 60% of his sales are paid by wire transfer, and he offers a 3% discount on such bank-to-bank payments. The remaining 40% of purchases are made with payment cards.

Union Diamond, founded in 2001, has an inventory of 40,000 diamonds, priced from $300 to $500,000, although an occasional item can be priced at more than $1 million. The company has a showroom at its Atlanta offices, but completes 90% of its sales online. The privately held firm does not report its revenue.