(1) Any agreement entered into by an agent and the owner of property subject to Sheriff's sale, under which the agent is engaged to assist the owner in recovering surplus funds, is prohibited unless all of the following requirements are met:
(a) The agreement is in writing and duly signed and acknowledged by the owner;
(b) A copy of the agreement is filed with the Sheriff and the Law Department before any surplus funds are paid to the owner; and
(c) The agreement clearly states the fee or compensation to be paid, which shall not exceed fifteen percent (15%) of the value of the surplus funds.