When you sign up as a JVZoo affiliate or seller and list your country as the United States you will be required to fill out a W9, even if you only plan to sell your own products. JVZoo can only collect this information electronically so they have the ability to make it available to sellers that need to complete 1099's for their affiliates. W9's are submitted and stored securely. The only time it can be accessed is when you make a sale for a seller. Only sellers that you have made a sale for may access this information.
If you are being asked to submit a W9, and you are not a US resident, you are seeing the requirement because you listed your country as the US when you created your account. You can change your Country of Residence by going to My Account > Account Details and click the arrow to expand the Personal Information section then click the "Edit Information" button.
For any questions relating to tax law you need to contact your tax accountant. JVZoo cannot provide this type information.