Reduction or demotion shall be made only for one or more of the reasons given in section 124.34 of the Revised Code, except that voluntary written agreement by an employee to a demotion or reduction shall be considered a satisfactory basis for such action in the absence of evidence to the contrary. The salary of an employee following demotion shall be fixed by the director at the equitable rate, not to exceed the rate of pay prior to the demotion.