We polled some of the nation’s best jewelry trainers and salespeople to learn how to be a top performer. Hint: Product has very little to do with it.Delivering top-notch customer service is the most important aspect of selling, according to sales stars and training experts. It’s more important than retail location, more crucial than targeted advertising, and, arguably, more central to the deal than the product itself. In fact, adept salespeople maintain that the art of the sale all comes down to superior customer service.Customer care is also one of the hardest aspects of the business to get right—a ceaseless challenge with a continuous flow of variables as diverse as mankind. Too often, it’s overlooked.There isn’t a magic key to providing great customer ­service, say the experts. Rather, you need a knack for knowing when to ask questions, smile, or leave a shopper alone. Bein