How to get the lowest shipping rates on Shopify?

Shipping rates depend on the parcel's size, destination, etc., and the carrier. In order to get the best rates, many merchants use more than one carrier. They select the best carrier for each order. But it can be challenging to manage, especially if you have a large variety of products. You'll probably have to use a Shopify app like ShipperHQ, Pirate Ship, Shipstation, etc. for managing shipping rates and carriers. These apps let you set automatic weight thresholds for each one of your carriers. Give it a try. Good luck :)