Between a buyer paying at the door and a seller receiving a transfer, money passes through several hands and several days. Cash gets miscounted, an order gets marked delivered when it was returned, a partial payment gets recorded as full. None of this is unusual. What matters is whether it is caught.
Reconciliation is the control that catches it. Without it, a seller has no way to tell the difference between a fee and a loss.
Every order carries its collected amount through the system, so the settlement statement is built from order-level records rather than a warehouse total. Inventory is tracked at 99.6% accuracy, which is what makes the stock side of the same question answerable.