Turns out he was a bookkeeper and had just purchased an Apple IIe and wanted to use it for his clients. I knew nothing about accounting, he knew nothing about computers, so it seemed like a good match :)
Four weeks of spending free afternoons at his shop, and it was ready to go. He was happy and I had 200 bucks in my pocket. Life was good.
Almost 20 years later, I get a call from him. He says the program isn't working so well and he wants to upgrade. I'm like WTF? Does anybody in the universe still even have a working Apple II anymore? Why would he keep using something like that for 20 years?
He told me that as computers modernized, it became a bit of a status symbol to have an older-looking system spewing out reams of reports. His customers, who were mostly small construction companies and such, got the feeling of stability and security from something that was unchanged.
It is a very strange feeling to get a call about code you wrote a long, long time ago. If I would have had any sense, I would have realized from the experience that programming is normally an extremely tiny part of actually making a business work. But it took me many more years to figure that one out.