This isn't just a challenge for salespeople, but for the entire supplier organization. As a group, today's customers are not particularly fond of salespeople. Not all customers feel this way, of course. But even those who talk to salespeople have changed expectations. Today, that's a given.
Customers expect it.
What's really effective is exploring areas of opportunity with the customer. This requires asking the right questions, searching for ways to reduce the overall cost of procurement, or perhaps, helping customers with their marketing plans. They must offer more than competitive pricing. Here there's much to be said for electronic ordering, billing, and payment. You'll get different answers from most people you ask.