Staff inadequately trained to handle returns

I bought a 6pack of house brand full cream long life milk. Prod date 16-8-17. Upon opening I found the milk on the sour side of fresh in taste. Opened another - same. Took all 6 to return. Supervisor on duty smelled then tasted the milk and declared she found mothing wrong with it. I explained that I would not have brought an entire 6pack back if I did not find it "off"; and in any case surely it is my opinion as the purchaser and not open to debate? She allowed me to exchange for another 6pack of same. No acknowledgement of inconvenience to me. Very reluctant and while not rude, she was clearly put out by having to effect the return. Seems staff are not adequately trained in handling returns and complaints. Have never had to debate the validity of a return at say PnP or Woolies!