At the time of the hearing the department of inspections and appeals shall receive any evidence and listen to any arguments presented by either party relevant to the matter under investigation, and the burden of proof is not upon the person making the complaint. The complainant shall add to the showing made at the hearing whatever information the complainant then has, or can obtain from any source. The department of inspections and appeals shall propose just and reasonable rates, which may be adopted in whole or in part or modified as the state department of transportation determines.