To remove a product from the Marketplace or "My Retailers" sales channel:
Go to the Products page.
Select the product row(s) you want to un-publish.
Click "Update availability".
Deselect the channel checkbox you want to unpublish. To remove the product from the Marketplace only, and let your approved retailers keep selling it, only uncheck the Marketplace checkbox and leave the My Retailers checkbox checked.
Click "Update".
The select products will no longer be available on the deselected channel(s).