You may take a look at the CustomersViewModel and check the CollectionChanged event of the ObservableCollection Customers. The logic there is the one responsible for the inserting and deleting the items from the data source. Such event is not present for a IQueryable. Furthermore, it does not provide methods for adding and removing any item. Generally, the idea of IQueryable is to provide queryable data source and build query by expression tree. You may take a look at this article for further reference.
Considering the ability to cancel the changes, you need to implement IEditableObject Interface for your business object. You may run through this article for a hint.
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