Fascinating. How to handle the overhead of ordering
supplies, maintaining inventory, etc.? That requires people.
In Zazzle's case, they do it for you--essentially, they print on demand and then drop-ship the item directly to the person who's ordered it. You-the-designer set the price point, Zazzle takes a fixed cut in return for its services, and you get whatever's left over. In other words, you effectively pay a bit more to get the thing printed in return for them handling the supply, shipping, inventory etc. hassles for you.
Ah-ha. Capiche.
Darrell