At the Collision conference in New Orleans last month, I heard a marketing executive defend the practice of tracking consumers across their mobile devices. But then he offered some unexpected consumer advocacy.

Adam Berke, president of the advertising firm AdRoll, had spent the previous 15 minutes endorsing cross-device tracking as a logical response to the way we often start researching a purchase on a phone before completing it on a laptop or desktop.

Then he had some different advice for advertisers: Balance privacy with personalization, and protect the user’s “right not to be surprised.”

That “right” is hard to define

What would such a right amount to in practice? We already have a web in which ad networks can use cookies — tiny tags in ads that your browser downloads — to track our visits across sites. And those advertisers can then correlate that data with other identifiers, such as a phone’s electronic ID and your record of clicking on ads, to form a rich picture of your interests.

I followed up with Berke, who talked to me on the phone out of his San Francisco office to expound on the idea.

“You obviously want to do the right thing for both moral reasons and for business reasons,” Berke began.

In other words: Agencies don’t want to produce ads that are so shocking or creepy that they drive consumers to buy competing products.

“It’s something that we’ve talked about internally for a while,” he added.

But have those discussions provided an exact definition of the “right not to be surprised?” Not so much. Berke suggested part of that right involved retaining empathy for “the average person — not yourself as a marketing technology person, but what the average person would understand about online advertising.”

A privacy expert with a background in advertising couldn’t pin down the concept, either.

“‘Don’t Surprise People’ with what you are doing with their data has long been an informal guidance in the world of privacy, along with 'Don’t be Creepy,'” said Jules Polonetsky, CEO of the Future of Privacy Forum. “Back in my AOL and DoubleClick days, we would often turn down a proposed ad campaign, telling the business people that consumers would be surprised, or worse, creeped out!”

But, he continued in an e-mail, the squicks-us-out line shifts.

“There was a time when ad networks didn’t retarget users in a way that made people feel they were being followed,” he said.

Retargeting is the fine art of showing you ads at third-party sites for a product you’d checked out at a different site — see also, why looking at one refrigerator at Amazon ensures that every other ad you see elsewhere includes a pitch for somebody’s fridge. It’s a core part of AdRoll’s services.