AdvancedUser.php

<?php

class AdvancedUser extends User
{
  public function type()
  {
    return 'advanced';
  }
}

Product.php

<?php

class Product extends Model {

    public function user()
    {
        return $this->belongsTo(app('App\User'));
    }
}

User.php

<?php

class User extends Model
{
  public function type()
  {
    return 'basic';
  }
}

UserServiceProvider.php

<?php

class UserServiceProvider
{
  public function register()
  {
    $this->app->bind('App\User', AdvancedUser::class);
  }
}