A friend asked me recently, "What separates really good salespeople from merely average ones?"

I told him it comes down to one factor: knowledge of the customer. Prospective customers can sense very quickly whether you know enough about their needs to be able to offer what they want. Average salespeople use their limited time with prospects to sell them on everything a product or service can do, with predictably hit-or-miss results. Good salespeople focus on the particular feature that the customer cares most about. How do they find out what it is? By talking to people with specific knowledge of the industry.

I'll give you an example. At a reception recently, a salesperson for a software company approached me. He knew I was in the records-storage business. "Can I ask your advice?" he said. "I have a big appointment coming up with Iron Mountain that's taken me two years to arrange, and I need to understand what's going on there."

Iron Mountain is the giant of our industry, and it had a shakeup in April, with the former CEO, Richard Reese, stepping in to replace the man who had succeeded him just three years earlier. Reese put the digital branch of the company up for sale and made other changes that he said would increase Iron Mountain's return on invested capital. I knew what that meant. "They're selling into their unused capacity," I said.

"Explain that to me," he said.

"A brand-new warehouse costs me $5 million," I said. "So the first box I put on the shelf, I get 25 cents a month back from that $5 million investment." He laughed. "But if I can fit that box into one of my existing warehouses, almost all of that 25 cents goes straight to my bottom line. So if your software can help them track their unused capacity, that's what I'd highlight."

"OK," he said, "but I was thinking I could sell them on the savings. I can cut their costs by $200,000 a year."

"Well, Iron Mountain is a $3 billion corporation," I said. "I think saving $200,000 a year would be a secondary factor. I'd treat those savings as an added bonus." He thanked me and promised to let me know if he got the business.

Now, that is a good salesperson. If he had gone into the meeting trying to sell the cost savings, he would have gotten nowhere. Worse, he would have undermined his credibility, making it more difficult for him to sell the decision makers on the features they might really care about. By seeking out someone knowledgeable in the industry, he dramatically increased his chances of making the sale. Of course, there's no guarantee that he will be able to close this deal. What I can guarantee is that, over time, he will have a better track record than most of his peers.

Please send all questions and comments to AskNorm@inc.com. Norm Brodsky is a veteran entrepreneur. His co-author is editor-at-large Bo Burlingham. You can follow them on Twitter at @normbrodsky and @boburlingham. Their book, Street Smarts, is available in paperback.