Hearing procedure requires notice, allows further inquiry, and restricts fresh evidence and new grounds absent sufficient cause. The Appellate Tribunal must fix a hearing date and notify the appellant and the Commissioner, may order or direct further enquiry by the authority against whose order the appeal is preferred, and permits the Commissioner to be represented. The Tribunal shall not admit, for the first time, accounts or other documents on behalf of the appellant unless prevented by sufficient cause, nor allow new grounds of appeal at hearing unless omission was not willful or unreasonable.