All bids shall be opened on the date and at the place specified in the advertisement for the same and such opening and inspection of the bids shall be made by the purchasing agent in the presence of the board of supervisors or auditors or their representatives. The supplies and articles furnished under all bids and contracts shall be such as are called by requisition of the county officers or heads of county departments or institutions and equal to and of the same quality as the sample furnished the purchasing agent, and all supplies furnished by contract as provided herein shall be equal to the sample which may be required to accompany the bid. If the supplies delivered under contract do not come up to the sample, the purchasing agent shall refuse to accept the same. The estimates furnished said purchasing agent, as aforesaid, upon which he makes his advertisements and contracts, shall, as near as practicable, state the quantity and quality of the articles and supplies needed, and when possible, the brand of the same, and copies of such estimates shall be filed with the county clerk or, in counties having a board of county auditors, with such board, and be opened to public inspection.