Incorrect Best Before Dates on C***** Milk

Two days ago I purchased a 2 litre of milk on the 19th of November, from the PNP express at ferndale in Randburg. Today I opened the milk for guests and the milk was off, really embarrassing for me, although the Best before date is for the 27th of November. The date of the best before was definitely incorrect. How will I bypass this problem in the future, do I open a milk every time of purchase to smell if the milk is off?? The date of the best before date was incorrect!!! I hope my guests do not get sick from the off milk that was used!!