Ok, I'd like to summarize the theories.
He rides with his motorcycle to the city. Obviously he doesn't do this during the day, but maybe he drives to a 24/7 store at night. I could imagine that.
I could also imagine the online shop and I think straight ahead and wish that we could also get a computer to cover our needs online. That would be very bad times for Pierre with Joja, the night market and an online shop. On the other hand, also very realistic.
And as I mention Pierre, I also adhere to the fact that this dubious guy sells more than what we see.
The traveling merchant as a resident dealer? I like that but all the stuff there must be overpriced maybe for the service to carry that stuff to the valley. Most of the items could be out of Zuzu and maybe you'll get them there to a "normal" price. (We really need Zuzu to explore.)
And now I think the thought of the own tobacco plantation is the most unlikely. ^^
Edit: I forgot the train. Maybe this is one reason why he is often at the train station. Waiting for supplies. But I usually only get coal there and you can't smoke it. :D
Edit2: This is not the end of the thread. Just a summary in between. ^^