I think you're talking about a short story called "Rain, Rain, Go Away" by Isaac Asimov. It was published for the first time in 1959 as part of the collection called "Earth Is Room Enough." However, the story's plot doesn't exactly match the one you described. In this particular story, the Llewellyn family notices that it's always raining over their house while it's dry everywhere else. They eventually discover that their neighbor, a seemingly ordinary man named Angus, is actually responsible for this unusual localized weather pattern. Angus confesses that wherever he goes, rain follows him, and he's learned to accept and adapt to this peculiar condition. However, the story doesn't involve him offering his rain services to farmers. It seems like your description might be inspired by different elements from classic science fiction stories, though I'm not aware of a story that perfectly fits all your criteria. Would you like to hear about similar stories or themes? Let me know!