(a) The following persons shall not purchase property sold in the action directly or indirectly:
(1) The referee.
(2) The attorney of a party.
(3) The guardian or conservator of a party, unless for the benefit of the ward or conservatee.
(b) All sales contrary to this section are void except that a sale to a bona fide purchaser following a sale contrary to this section shall not be disturbed.