We had a problem with syncing our orders with Woocommerce. We also experienced double listings once everything was synced. Since we were new to both Woocommerce and Shippo, I was concerned about being bounced back and forth.
So we contacted them immediately. They immediately recognized the problem and they helped us understand it. Although we are experiencing some residual issue, they have made sure to address all of our issues. All the while we experienced no downtime.