The customers at Columbia Bank’s branch in Towson, Md., are fairly predictable.

Most of them are residents of Edenwald, a 400-person retirement facility in the town, and they typically use the branch to deposit pension and Social Security checks and withdraw money once or twice a month to cover expenses. To Suzanne Borkowicz, the branch’s manager and one of its two employees, these people are like neighbors.

So last spring, when Ms. Borkowicz noticed one of her elderly customers making a larger-than-normal withdrawal for the second time that week, she drew her aside and, as she gave her the money, asked a few subtle questions.

“I know personally all of the residents and their families, and I knew for this individual to withdraw large sums, it was out of the ordinary,” she said.

But the customer didn’t say there was anything wrong. She was wiring the funds to a nephew in Canada, she told Ms. Borkowicz.

Ten days and two sizeable withdrawals later, she told Ms. Borkowicz the truth: She had won $250,000 in the Canadian lottery and had to pay taxes on the windfall up-front. In fact, two people were coming to her apartment that day to collect.

After convincing the customer that it was a scam, Ms. Borkowicz notified the directors of the retirement community and helped foil the scheme.

“I was very glad,” she said. “It’s frustrating to know something is going on and not be able to do something about it.”

In October Ms. Borkowicz was awarded the Silver Good Citizenship Medal by the Baltimore chapter of the Sons of the American Revolution.

The lesson for other bankers, she said, is simple: “Keep your eyes and ears open and know your customers.”

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