Rob,

Anything the user sees ro must react to is the responsibility of the User interface, that's why it has that name (it interfaces with the user). If you have a delete button its responsibility to provide a mechanism for a user to request a deletion. If you want that deletion confirmed before doing it then you must ask the user for confirmation (also the responsibility of the user interface) so you do it in the user interface before you call the business object and request the deletion.

Once the UI has confirmed the action is desired then you request the business object for the service. It does what it can and returns a vlaue telling you if it was successful or not. You can also have the business object have a property that it uses to store the last error that occured and a method for retrieving the last error so your UI can get detailed information about any failures.