services.cs

public interface ICustomerService
{
    void MakeCustomerPreferred(Guid customerId);
    Customer GetCustomer(Guid customerId);
    IEnumerable<Customer> GetCustomersWithName(string name);
    IEnumerable<Customer> GetPreferredCustomers();
    void ChangeCustomerLocale(Guid customerId, CultureInfo newLocale);
    void CreateCustomer(Customer customer);
    void EditCustomerDetails(CustomerDetails customerDetails);
}