All commodities bought or sold by weight or measure shall be bought or sold only by the standards established by this chapter, unless the vendor and vendee otherwise agree. Sales by weight shall be by avoirdupois weight unless troy weight is agreed upon by the vendor and vendee.
All commodities bought or sold in package form shall be labeled in compliance with the general provisions for labeling provided for in sections 189.9 to 189.16, unless otherwise provided for in this chapter.