Check out our tutorial video on how to create a private product listing:
To create a private product listing for a customer you can either start with a brand new listing or you can duplicate an already existing listing and edit the details for this private listing.
After you create the listing you will change the listing STATUS from DRAFT (the default status when a product is created) to HIDDEN.
Now you can click the Settings symbol and Preview the listing on the marketplace where you can copy the URL and share that with your customer.