When you have more than one Shipping Rule saved in Solid Commerce, the system searches through your list of rules from top to bottom until it finds a rule that applies to the order you are shipping.
We have some predefined filters that prioritize the rules for you. The filters do a good job, but sometimes you might end up with a rule that is lower on the list than desired.
EXAMPLE: Let's say you have a rule that requires all packages over 2lbs to be shipped FedEx Ground. You also have a rule that requires orders to PO Boxes to be shipped USPS Priority, no matter how heavy they are. If your FedEx Ground 2lb rule appears higher on your list of rules than your PO Box rule, you will end up printing FedEx Ground labels on PO Box orders.
To manually adjust the order of your rules, in Solid Commerce -> Admin menu -> Manage Shipping Rules ->> Click on the name of the rule you wish to move. Click on the up or down arrows to the right of the list of rules to change the priority.