Starbucks revealed just how far it is ahead of everyone else in mobile payments last week, and the answer should be both terrifying and heartening for other retailers.

The coffee-house chain said its customers do 2.1 million mobile transactions at Starbucks every week—about 5% of all its sales transactions in U.S. stores.

That’s the terrifying part: No other brick-and-mortar retailer comes remotely close to those numbers in mobile payments. The heartening part: It’s possible. Despite all the wheel-spinning from PayPal, Google and Isis when it comes to getting customers to use mobile payments, it can be done. And it’s not something unique to Starbucks customers.

In the company’s earnings call on January 24, Starbucks chief executive Howard Schultz ran through the type of numbers that most chains can only dream of for their mobile efforts: “Our Starbucks card is more popular than ever today, accounting for 25% of U.S. tender, and an increasing portion of Starbucks card transactions and sales are being paid by using our mobile payment apps, with mobile payments now accounting for nearly 20% of overall card transactions. Over 7 million customers now use one of our mobile payment apps, translating into 2.1 million mobile payment transactions each week, with hundreds of thousands of additional Starbucks mobile app downloads each week.”

It’s not hard to figure out why the Starbucks mobile effort is snowballing at this point. Once you’ve got millions of mobile transactions per week, customers see other customers flashing their phones to pay and the system sells itself to new users.

It’s also clear there’s nothing special about the Starbucks payment app, which is essentially a smartphone version of the Starbucks stored-payment card, along with a feature to add money to the stored-payment account from a credit or debit card. This is plain-vanilla mobile payment technology.

Nor is there any big secret under the covers. If there were, Safeway would know—it’s been handling the transactions for Starbucks kiosks in its stores for more than a year. There’s no indication Safeway has become any more savvy about mobile payments.

Lots of chains with zero mobile-payments success have customers as young and affluent as Starbucks, and those customers have the same phones, so that can’t be it.

True, Starbucks started trialing mobile payments in 2009, but by the next year it was expanding rapidly. Clearly, this shouldn’t be taking Google and PayPal so much longer to get results.

And although it doesn’t hurt that the Starbucks system is tightly married to its loyalty program, virtually every big mobile-payments approach is built around loyalty and CRM. That by itself hasn’t done the trick.

Then why is Starbucks so successful at mobile payments? Is it because Starbucks already had trained its customers to use the stored-value cards and just convinced them to switch over to the same thing on phones? That’s an easy answer, but it’s meaningless. Every chain’s customers are already trained to use plastic cards for payment. The hard part is getting them to switch to using their phones.

Is it because of signage that tells customers about the mobile app, or baristas that push customers to try it? One of our co-workers gets coffee from five different Starbucks stores and doesn’t remember ever having seen a sign or heard the mobile app mentioned by an associate.

Then again, he’s not a classic Starbucks customer. He doesn’t know his barista’s name or sit at a table nursing his drink as he works on his laptop. (In fact, he admits he only goes into a Starbucks to get a very large coffee that he later pours into another container that he finishes off over a day or so. No wonder the baristas won’t talk to him.)

But regular customers do have a relationship with their baristas. Whether they know the barista’s name, their faces are familiar. That familiarity breeds trust. And that trust means that if a barista suggests trying to pay with a mobile app, the customer is much more likely to try it.

And once the regulars start doing it, you don’t need signage. You’ve turned your key customers into walking ads for mobile payments. They use the system. More casual customers see them using it and try it. Not every customer keeps using it, but enough do that it gets momentum—the one thing most mobile-payments schemes don’t have.

But that wouldn’t transfer to, say, PayPal’s in-store payment system at Home Depot, would it? It could. Some contractors are in there every day, and they know which associates have a clue—including deep knowledge of what’s needed on a job site, what Home Depot has and what the store can get.

Maybe the only reason those contractors aren’t using PayPal is because an associate they trust hasn’t suggested it.

Maybe the same is true at Toys’R’Us, where mobile payments seem like a perfect fit for gadget-happy customers and every point of sale terminal is also wired for PayPal. Or any of the sports or apparel chains where Google Wallet has a foot in the door but can’t seem to get any traction in customer usage. Or all those chains that have signed on with MCX, once it finally rolls out its mobile-payments system that on the surface looks suspiciously like the Starbucks approach.

No, it might not work. But what’s clear is that it has worked for Starbucks, and nothing that any other retailer or mobile-payments player has tried has come anywhere close to Starbucks’ success.

And until other chains start trying what actually works, mobile payments everywhere but at Starbucks will keep spinning its wheels.

StorefrontBacktalk

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