This story happened to a relative of mine. He has little kids. Like all kids, they are not very careful bike riders. And that’s why their bikes have flat tires.
One day my relative took a flat tire to a tire mounting service. They fixed the bike tire and didn't even take any money. After a while another tire (or the same one) deflated. The relative went to the tire mounting service again, gave them the wheel and said that they ought to charge him some money that time. Otherwise he would be offended. The mechanic nodded. The relative left the service to run some errands, so that the wheel had to be picked up by his wife. Later, the relative asked her, 'Have you paid?' She said, 'I tried to, but the mechanic refused to take the money.'