What really impressed me was the need to be able to run the entire Rube Goldberg machine backwards. You really want to have "the order" as static as possible,

What really impressed me was the need to be able to run the entire Rube Goldberg machine backwards. You really want to have "the order" as static as possible, for "the invoice" there is even legal obligation. Then it goes something like... I bought 5 and got a discount but I want only 3 and ohh there is a typo in my name and one in my address - sorry about that. No problem, you credit the invoice, make a new one for the same amount with the name and address correction, then you wait for the items to be returned and checked and credit it again, make a new invoice again. The return shipment stays in limbo for a while, they order 5 more, one arrives broken, they want a refund rather than a replacement. With 2 delivery dates the system doesn't apply the 5+ discount.... and all of a sudden you have tons of transactions and "paperwork" for what you initially imagined to be 2 simple orders. They also forgot their password so they made a new account using a different email address. Looking over the logs a year later it is hard to figure out why they got a discount for just 3 units.