Elmer Wheeler was a marketing genius of the 1930s. Of course you've heard the expression: "Sell the sizzle not the steak." You may think that's so proverbial that nobody knows who said it first. Not so - Elmer Wheeler coined that phrase more than 70 years ago.

He coined many phrases, by way of marketing rules, and they made billions of dollars for Wheeler's clients.

Wheeler started as an ad salesman for several newspapers, trying to convince retailers that an ad in his papers would drive people to their stores. This, the retailers didn't doubt, but people just visiting their stores was not enough-they were not buying. Sound familiar?

This is an age-old, constant problem. People visit stores or they log on to internet sites. But very few of them actually buy anything. Interest, but no sale-why?

That's what Wheeler decided to find out. During 10 years of research, Wheeler tested over 105,000 words and phrases on more than 19 million people. His exhaustive research is simply and actionably summarized in his 1937 book, "Tested Sentences That Sell."

Wheeler derived a number of critical "Wheeler Points." Here's one of them? Always give the prospect a choice. But make it a choice between something and something, said Wheeler, not between something and nothing. He gives the example of the restaurant business? If the waiter asks "Wine with dinner?" the answer is NO most of the time. But when he asks, "Would you like red wine or white?" then wine sales take off.

Here's another of his case histories. A pharmacy was having difficulty selling shoe insoles. After some trial and error, Wheeler got the salespeople to ask the customers: "Are you on your feet much?" Then they'd hand them a shoe insole and say: "This will ease your feet. It's made especially for people who are on their feet a lot." These words sold hundreds of insoles every week.

Or look at this one. Wheeler dramatically increased sales of oil at a garage. He tried and tested 100 sentences until he found one that really worked. Salesmen were asking the naive question: "Can I check your oil?" This nearly always resulted in a "no" reply. So Wheeler tested and found that the question "Is your oil at the safe driving level?" worked 58% of the time.

Wheeler's principles are as unchanging as the problem of high traffic and low sales. It's the same problem, whether it's the sales script on a showroom floor or the copy on a landing page. Wheeler's "tested sentences" will keep on selling just as long as people keep on showing up but not buying. The right words really are magic, and the right questions get the answer YES.

What questions are you asking your customers?