He is not thanking them for paying. He is thanking them for trusting. For carrying the weight alongside him.
On the third day of the crisis, Señora Ana, who ran a tiny comedor (a soup kitchen disguised as a diner) in the barrio, arrived with a plastic bag of devalued pesos. She was crying. "Don Celso, I need two sacks of rice. I have thirty children to feed. But this money… it's paper. It’s nothing." comercial garcimar
Don Celso untied the sack of sugar. He scooped a cupful into a small paper bag, handed it to the man, and pointed to the broom in the corner. "Sweep the back aisle. Then you can go. And tomorrow, you come back. We will find you work." He is not thanking them for paying