– Ketul Poshia stiffens his posture in his chair. He flashes a smile that seems to come far too easily to him. And then Poshia, a customer service representative with Amazon's Mayday video tech support, clicks his PC mouse to let an Amazon customer's frustration in.

A woman's voice comes over Poshia's headset, a bit confused about why she isn't able to get e-mail on her Fire tablet.

"I might have pressed something, but I haven't gotten e-mails since yesterday," the woman tells Poshia.

While the customer can see Poshia, in a compact cubicle with an Amazon-branded backdrop behind him, Poshia can see only the screen of her Fire tablet. It's clearly not the first time Poshia, who's been working at the customer service center since 2013, has dealt with missing e-mails, and his diagnosis is quick.

The caller recently changed her password for her e-mail provider but hadn't updated it on her tablet. Poshia walks her through the process and, within a few minutes, her old e-mails flow onto her Fire.

Amazon.com founder and Chief Executive Jeff Bezos has said that customer contact with Amazon, such as the one over missing e-mail, usually represents a "defect" in the online retail giant's operations. But those contacts are inevitable. That's why Amazon has a team of more than 500 here, in this city 180 miles southeast of Seattle, answering calls, replying to tweets and chatting via video to salve customers' anger and resolve their problems. And the company has added hundreds more temporary reps for the holiday season.

There's no shortage of problems. The center, one of six Amazon has in the United States, responds to thousands of customer calls a day, according to the Seattle-based company. Often, customers want tech support for Amazon's various devices. Sometimes, they need help clarifying bills. And plenty of times, customers want to know why their packages are late, and when they can expect delivery.

And yet, with so many "defects," Amazon consistently ranks among the top retailers when it comes to customer satisfaction, from organizations such as customer research firm Temkin Group, Zogby Analytics, and the Institute of Customer Service in the United Kingdom.

To Amazon's many critics, that might seem anomalous. Independent booksellers, whose businesses Amazon has helped undermine, often cite their personal touch with recommendations.

Bike shops, electronics stores and clothing boutiques often hire specialists who can guide shoppers to the right product, personalization that's hard to come by at Amazon, where recommendations are algorithmic.

But Amazon's customer service contacts generally come after a sale. At that point, customers aren't seeking personalized help to make a shopping decision.

"What most call centers are judged by is call efficiency," said Forrester Research analyst Kate Leggett. "It drives the behavior of trying to get the customer off the phone quickly."

Amazon, though, doesn't measure its reps by the speed with which they dispatch calls. The metric it uses is "negative response rate" or NRR. At the end of each call, reps ask if they've resolved the problem. Each "no" counts as a negative response.

Darrin Scharffenorth, the senior site leader of the Kennewick center, said calls generally get negative responses 5 to 7 percent of the time, though the numbers can run higher for new products and during periods of poor weather, when deliveries are delayed.