Cafepress.com provides a "warehouse" of products and sets its price for each item.  When an item is purchased, Cafepress pulls that piece out of its inventory, adds the graphic specified by the Grover store, and ships it out. Revenue from sales is collected by Cafepress.

The Grover Store does not maintain any inventory; the only investment is the time involved in developing the graphics and deciding what to sell and what graphic to specify for each.