Can I choose which carrier I ship with?

In the app: Settings, then Postage carrier. Unpinned, each label takes the cheapest rate across USPS, UPS, and FedEx. Pinned, each label takes the cheapest rate from that one carrier.

The choice changes what every buyer is quoted across your whole catalogue, so once set it is locked for 7 days. If the pinned carrier cannot serve a particular shipment, the cheapest available rate is used instead so the order still ships.

USPS is usually the most expensive option for the big, heavy boxes most wholesale lots ship in. UPS and FedEx are often noticeably cheaper at that size.