How to properly structure multiple user types?

So i'm building a database for an app/website. It's essentially a e-commerce marketplace/platform where a brand can sign up to upload their products and customers can also then sign up to purchase any products from any various brands. A brand and or employee cannot be a customer A customer cannot be a brand This is the structure I have so far, but it seems to me that from this diagram it implies that a user can be a customer, brand and brand employee at the same time. Is there a better optimal structure for this?