That's different from what the OP is talking about. You raised prices and volume went down. He raised prices and volume went UP.
At a glance the simple explanation, having some experience in marketing myself, is that $19.99 is a magic price point- 9/10 times you will not see any price point on an infomercial that isn't $19.99 or $19.95. And it's because it's a magic price point. Hard to explain but it works.
If he had gone from $19.99 to 39.99 or from 4.99 to 9.99 it would not ave had this effect- his volumes would have gone down. But if you want to sell something at $14.99, 9.99 or 24.99, don't do it- just sell it at 19.99.
At a glance the simple explanation, having some experience in marketing myself, is that $19.99 is a magic price point- 9/10 times you will not see any price point on an infomercial that isn't $19.99 or $19.95. And it's because it's a magic price point. Hard to explain but it works.
If he had gone from $19.99 to 39.99 or from 4.99 to 9.99 it would not ave had this effect- his volumes would have gone down. But if you want to sell something at $14.99, 9.99 or 24.99, don't do it- just sell it at 19.99.