An oral binder is a legally recognized temporary contract that provides immediate insurance coverage before a written policy is issued. While oral binders are valid in all Canadian provinces, their reliability depends entirely on whether the intermediary actually has binding authority from the insurer. If the broker or agent who gives the oral binder does not have the authority to commit the insurer, then the binder may not be valid, and coverage may not exist. This makes lack of authority the primary risk associated with oral binders.

Option A is incorrect---oral binders are legal across Canada.

Option B is incorrect---a binder cannot override policy warranties; it simply provides temporary coverage.

Option C is unrelated; privacy documentation is not what makes a binder valid or invalid.

Thus, the key problem is that the intermediary may not have binding authority, making D the correct answer.