This is a really neat idea. The most important issue was probably the shipping cost which you seem to have solved with a flat rate. One issue I think you might

This is a really neat idea. The most important issue was probably the shipping cost which you seem to have solved with a flat rate. One issue I think you might run into and might want to think about, is what happens when a customer needs to cancel a shipment or make a change of address? It might be worth it to figure out a system of notifications with easy routing for customers to engage customer support with the carriers. Im also curious as to what carriers you are supporting? Is it carrier agnostic, so to speak? It sounds like it could be abstracted away from the carriers altogether through an API that merchants would connect to? FYI, I work for a UPS on internal applications, but while going through school worked in operations so I have a pretty broad spectrum and understanding of package movement.