The big problem with many in-store campaigns is getting stores to actually carry them out, then knowing which among the tens of thousands of stores nationwide actually have done so.

So Sergio Zyman, former Coca-Cola Co. chief marketing officer and longtime marketing consultant and author, is backing a mobile app called GoSpotCheck, which allows just about anyone -- from field merchandisers to someday a company's non-sales employees or a brand's shoppers and Facebook fans -- monitor what happens in stores.

The app, which enables users take photos and answer simple questions, has been adopted by a top-50 consumer-packaged-goods company and a top-15 quick-service restaurant chain, said GoSpotCheck CEO Matt Talbot.

It also seemingly has the potential to disintermediate the in-store auditing forces of big brokerage firms such as Acosta, Crossmark and Advantage Sales and Marketing. Executives of those firms either declined to comment or didn't return calls and e-mails for comment by deadline.

While GoSpotCheck is starting with employees, "we're eventually going to recruit consumers to do this in a mass way," Mr. Zyman said.

What would make fans or shoppers want to do that ? Rewards -- either in the form of discounts or merchandise, Mr. Zyman said. As it stands, mystery shoppers work for as little as $12 a month, plus free merchandise in some cases, according to some bloggers. And for brands, many of which have millions of Facebook fans seeking deals, finding enough to cover just about any store in the U.S. shouldn't be that hard.

Data security may be a concern, Mr. Talbot said, but GoSpotCheck gets around that by not storing any data on phones and uploading it instantly.

"The thought is that these bigger brands have incredibly large numbers of people in the field, and if they can have the tools to verify that perishable promotions like the big Fourth of July event for Coke are really happening, then you can remove that extra layer of having someone do an audit," Mr. Talbot said. "You have GPS-verified data and photos to prove it was done in minutes, rather than weeks."

One customer in beta test already used the tool to get an additional 5 million in-store impressions from convenience stores due to lack of compliance with a promotion, Mr. Talbot said, and he expects the data could eventually work their way broadly into pay-for-performance deals with retailers.

"You spend six or eight months trying to develop a promotion or a new-product launch, decide where you're going to place it on the shelf, then you launch and hope the retailer or the fast-food franchisee are actually going to put it in front of the consumer when the advertising is on," Mr. Zyman said. "But you don't know."

GoSpotCheck also allows marketers to get real-time information on ambush marketing during big sponsored events such as the Olympics or Super Bowl, he said, adding that the data arrive fast enough that marketers may be able to fix problems rather than just complain about them after the fact.

"The activity happens today with mystery shoppers," Mr. Zyman said. "But they're often inaccurate. They're not pervasive, and you don't get the information in time to actually correct."