A good case in my experience was Radio Zaracay in what was formerly called Santo Domingo de los Colorados in Ecuador. This was a higher powered 120 m band station that had rural audience all across the banana growing Andean foothills of Ecuador. It was used to advertise farm implements, transport services, vehicles and all manner of consumer goods. But a large part of its income came from "mensajes" or "messages" which were paid notes to far off listeners with no phone service.
Examples were "Attention on the El Porvenir hacienda in Puno parish of the province of Los Rios. Please take a donkey into town tomorrow at 1 PM as the boss arrives on the bus at that time". Others could indicate how much to harvest, the death of a person, a marriage or just be a "dedication" from one person to another. These messages were more expensive than agency commercials.
At one point, Zaracay may have been the highest billing station in the country. It was, for most of its most successful years, principally with short-wave only and just a low power AM for local service to the small city of Santo Domingo.
There were several other such stations in rural or agricultural areas that made a fortune. I even used my Quito AM on 590's big coverage to also sell "mensajes" and billed more from that then from paid commercial spots. For most of us, that income was all cash and might have had a hard time making it onto income statements.