Usually, companies fixate on the gap between how much their products cost to make and how much they charge for them. But you should also focus on the gap between your price and how much value customers think it delivers, a concept known as perceived value.

Companies often assume that if sales are slow they need to cut prices. But more often, Dearing says, "If nobody's buying my product, it's because the gap between price and perceived value either doesn't exist or it's not large enough."

Evernote is trying to measure that gap. The company's Premium accounts currently cost $5 a month. Libin recently started testing Evernote's price in some countries to find out whether that's cheap or expensive relative to perceived value.

"It's possible that in some countries, like India or China, $5 a month is too expensive," Libin says. "For the U.S. or Japan it may be that $10 a month is still cheap."

You can increase perceived value with better marketing. EBay, for instance, offered a feature from its inception that for 25 cents allowed people who sell products on the site to add a photo next to their listings. It wasn't used much, Dearing says.

But it turned out that sellers who included the pictures had much higher click rates and tended to command a higher price for their goods. EBay started to market this data along with the feature.

With the benefit of the sales data, eBay's sellers saw that the pictures helped solve a problem and their perceived value skyrocketed.

Because it didn't cost eBay 25 cents to host a photograph, the feature, along with other optional upgrades, eventually generated hundreds of millions a year in pure profits, Dearing says.