A retailer with an ad business sells its shelf space twice

Brands have always paid the retailer to stock their products. Now they also pay to be seen by the retailer's shoppers, online and in store, and that second sale carries far higher margins than the first.

The shelf, sold again

A retailer knows what its customers buy, when and how often. That data makes its advertising unusually valuable to brands, because the ad appears where the purchase happens. The revenue arrives without new inventory, new stores or new staff, so most of it falls through to profit.

For a business with thin retail margins, even a modest advertising line changes the profit picture.

What I'm watching

• Advertising revenue growth
• The number of brands buying ads beyond the largest suppliers
• Membership and marketplace growth, which enlarge the audience

Where I stand

Long, on a high-margin business growing inside a low-margin one. It is the part of the story the traffic numbers do not show.

What would change my mind

Advertising growth that depends on a handful of large suppliers. A business funded by the retailer's own vendors can stall when those vendors cut budgets.