User model inherit Seller model or vice versa?

So all Sellers are Users, Users can be Sellers in this marketplace

Should Seller be on top and inherit to User or the other way round?

I found it weird when doing a Session login, I’ve to call
Seller.has_sold? even
though all they are all Users to begin with, but I can’t call
User.has_sold? since the method is not in User.rb.