As the claimant on an order, you have access to the, green, "Finalize Order" button (see below):

When you're ready to complete your order, click the "Finalize" button.  This will display the following pop-up box with several user options:

Action: Display invoice to be created once order is finalized

Action: Make changes to order prior to finalizing

Action: Finalize Order

Action: Cancel Finalize / Go back to Order

The status of an order after Finalizing depends on the balance at the time of Completion.

Balance Due on Order: Status = Balance Due
No balance: Status = Completed
Refund Due to Customer: STATUS = Refund Due