Pay attention to condensation in packaging in the supermarket
For foil-wrapped food, make sure that there is no condensation inside the packaging as this is a sure sign that the storage temperature of the product was not constant (which it should be).
This can lead to a rapid mold, although the product should be still edible from the date.
Always check the freezerware for packaging damage, because of freezer burn and also there: no condensation!
View packed supermarket fruits and vegetables from below as moisture and mildew are often lurking below.