Sometimes, customers will come in to talk about a request or a problem after they have already spoken to another employee over the phone. It’s a bit like asking mom for permission when dad has already said no, and younger tellers may find themselves in the mom role. “We keep notes in the computer, so the new person has a heads-up on what is going on and what to do about it,” said Jessica Gleason, another Digital summer employee. “People will kind of elaborate on stories to try to get their way.”

Other times, they throw themselves on the mercy of a teller or member service representative. Bailey Griffith, who is working this summer at Ideal Credit Union in Woodbury, Minn., says he witnesses this a lot with customers who are trying to avoid paying penalty fees. “As a credit union, we have more leniency,” he said. “But if it’s happening every week, two weeks or month, and we’ve refunded it before, you know what’s going on. Some people kind of get angry about it, but if we refunded everyone’s fees, then what is the point of having the fee?”

Some, like Ideal, have partnerships with local high schools and set up limited-service branches on their campuses. That’s how Austin Raebel came to the attention of Ideal executives. The son of a business teacher at the local high school, he took a keen interest in the school-based branch, and the savings- and credit-building products that it offered to his fellow students.

Now, he’s in his third summer working at the full branch in Woodbury, earning $14 to $18 an hour, depending on which department he’s assigned to. “It’s people of all ages,” he said, describing his customers now. “I gave one member a new-car loan, and at the end, he said he had to ask how old I was: 24? 22? It was so awesome to engage in an intellectual conversation about lending with a 40-year-old when I was 17.”

He also managed to cross-sell the customer on a new checking account. “From a departmental standpoint, they fight over where Austin gets to work,” said Alisha Johnson, senior vice president for marketing, sales and service at Ideal.

Given their exposure to dozens of people’s financial lives each day, summer tellers can’t help picking up tips that they can apply to their own experiences. Ms. Matson of the G.E. credit union, who still works the teller line from time to time, said she liked to tell new employees about two customers she encountered within one short period of time.

“There was a fancy-looking person — a woman with her hair and nails done, and jewelry — and you could tell she had spent a lot of money on herself,” she said. “I pulled up the account, and there was no money there, and her loan was three months past due. Then there was the guy dressed like ‘Farmer Joe’ with a stalk of wheat he was chewing on and a bushy beard and dirty fingernails. He had millions.”