Scan packing box and weight at the PACK stage to determine shipping method
Scanning a box and total weight at the pack stage (which then determines volume and weight) to give a correct shipping method.
This would also serve as a double check to make sure all items are packed. At this weight check stage, it would bring up an error if the weight was over or under what it thinks it should be, within tolerance.
Then the shipping label is produced, as it now has the volume and weight.