User schema for different profiles

Hi,
I have another question about User schemas. Say, I have an eBay or marketplace type app, and a user who initially registers as a buyer on the site. In the code, there is a User schema with typical fields: :name, :string and :username, :string and a schema for BuyerProfile with the usual fields: delivery_address_1, delivery_address_2, delivery_zip_code, etc., and User has_one BuyerProfile profile relationship. I also create a BuyerProfile ‘belongs_to’ User relationship.

Later, the same user becomes a Seller as well, and then should have a has_one relationship with SellerProfile (SellerProfile schema could include fields like :tax_code, :string, etc.).. Is it preferable (scalable?) to maintain a user schema for some users, who could either have a buyer profile, or seller profile or both, as I can see that parts of the code will always have to do checks such as “if user has a buyer profile, then do this or show this…”? Or is it better to define a Role schema of Buyer, Seller and BuyerAndSeller and make a user belong_to a Role?

Thanks!