“There is only one boss—the customer,” Wal-Mart founder Sam Walton famously wrote. “And he can fire everyone in the company from the chairman on down, simply by ­spending his money somewhere else.”Walton was a titan of industry, but his sentiment rings especially true for independent retailers, whose businesses are based on the quality and quantity of their customer relationships.A well-oiled customer service machine maintains and augments a retailer’s stable of good clients. But the practiced graciousness of even the most experienced sales manager can be tested by the demeanor or demands of a cranky or ill-informed customer. Below, a handful of fine jewelers share how they cope with some of retail’s stickiest quandaries. iStockphotoRing shoppers are notoriously nervous. Think of it this way: You’re helping him pick a ring, not selling him a ring.1. What’s the best way