What are these installment savings products guaranteed at a minimum of 6% by major banks?

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When you go to large exhibition halls, there are people who set up booths unrelated to the exhibition
and run sales pitches claiming a minimum 6% guarantee for 3-year maturity terms of 30 million, 60 million, or 90 million KRW.
Yet, they use titles like ShinX Bank or KookX Bank, making it look like they are commercial banks.
When I ask them, they say it is an installment savings product with a minimum 6% guarantee...
I find myself wondering if such a 6% guarantee is even possible for those amounts.