
Here's what I did to be able to have this amazing profit.
1) Build a warehouse, and use a seaport supplier (I chose Gold). Have 7 "inventory" or whatever you call it, 1 input and 1 output.
2) Build a second warehouse, use the same build plan, but instead of linking the seaport as the supplier, link the first warehouse.
3) Repeat step 2
4) Repeat step 3
etc. etc.
Eventually I decided I wanted to try something a little different, so I built a factory, made tablet computer, maxed the price, and then did the same thing as above. By doing this, every consecutive warehouse was bringing in even more money. As of the Save Game (LINK), the most expensive tablets are over $60 million per unit, and my scheme is making me $246 billion profit.
This can only sustain itself if I keep building warehouses and buying from the previous warehouse. If I stop building warehouses, eventually it'll all come crashing down.
Summary? I think this is a bug, not because it's an error or anything, but because in real life, I'd be losing money since I'm not selling my tablets to another company, or to any consumers.