How do I delete a retailer connection on Shopify Collective?

From Retailers > Connected in your Collective: Supplier sales channel, select the retailer, click Delete retailer, optionally report misconduct with a message, and confirm. This immediately breaks the connection, sets that retailer's imported product inventory to 0, and notifies them by email. It's best to contact the retailer beforehand to settle any payments owed and agree on how to handle unfulfilled orders, since order syncing (including tracking numbers) stops within minutes of deleting the connection.