This, unfortunately, can’t happen. The reason for this is that, if the vendors won’t be able to see your Instagram posts then they will not be able to run the campaign. You don’t have to stay public always if you don’t want to obviously. But you must set your profits to the public before you place the order. You can set it back to private till the next order. Also, note that you shouldn’t revert your account to private in the middle of the campaign. Doing so will stop the comment delivery process completely.