(1) Before making any purchase or sale, the purchasing agent shall give opportunity for competition, under such rules as the commission may by ordinance establish.
(2) Supplies required by any department or office of the municipality may be furnished upon requisition from the stores under the control of the purchasing agent and whenever so furnished shall be paid for by the department or office furnished therewith by warrant made payable to the credit of the store's account of the division of purchases and supplies. The purchasing agent shall not furnish any supplies to any department or office unless there is to the credit thereof an available unencumbered appropriation balance sufficient to pay for such supplies.