Change Tracking an ObservableCollection

public class Customer : BindableBase
{
    private int _Id;
    public int Id
    {
        get { return _Id; }
        set
        {
            if (_Id != value)
            {
                _Id = value;
                RaisePropertyChanged("Id");
            }
        }
    }

    private string _CustomerName;
    public string CustomerName
    {
        get { return _CustomerName; }
        set
        {
            if (_CustomerName != value)
            {
                _CustomerName = value;
                RaisePropertyChanged("CustomerName");
            }
        }
    }
}

public class CustomerViewModel : BindableBase
{
    int _nextCustId = 0;
    List<int> _deletedCustIds = new List<int>();

    private ObservableCollection<Customer> _Customers;
    public ObservableCollection<Customer> Customers
    {
        get { return _Customers; }
        set
        {
            if (_Customers != value)
            {
                _Customers = value;
                RaisePropertyChanged("Customers");
            }
        }
    }

    private Customer _SelectedCustomer;
    public Customer SelectedCustomer
    {
        get { return _SelectedCustomer; }
        set
        {
            if (_SelectedCustomer != value)
            {
                _SelectedCustomer = value;
                RaisePropertyChanged("SelectedCustomer");
            }
        }
    }

    private bool _IsDirty;
    public bool IsDirty
    {
        get { return _IsDirty; }
        set
        {
            if (_IsDirty != value)
            {
                _IsDirty = value;
                RaisePropertyChanged("IsDirty");
            }
        }
    }

    public CustomerViewModel()
    {
        Customers = new ObservableCollection<Customer>();
        Customers.CollectionChanged += Customers_CollectionChanged;
    }

    private void AddCustomer()
    {
        // Use a negative Id for new customers. See RemoveCustomer

        _nextCustId--;

        Customer c = new Customer();
        c.Id = _nextCustId;
    }

    private void LoadCustomers()
    {
        // Call the data source to get the customers
        //var customers = _Dal.GetCustomers();

        Customers.Add(new Customer { Id = 0, CustomerName = "Customer 0" });
        Customers.Add(new Customer { Id = 1, CustomerName = "Customer 1" });

        // Subscribe each customer to a properrty change event
        foreach (var customer in Customers)
        {
            customer.PropertyChanged += Customer_Changed;
        }

        IsDirty = false;
    }

    private void RemoveCustomer()
    {
        _deletedCustIds.Add(SelectedCustomer.Id);
        Customers.Remove(SelectedCustomer);
    }

    private void Customer_Changed(object sender, PropertyChangedEventArgs e)
    {
        // A customer was modified. Do whatever you need here

        IsDirty = true;
    }

    private void Customers_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        // A customer was added or removed from the list. Do whatever you need here

        IsDirty = true;
    }
}