Three things every knit does, that most stores wait for you to discover. We would rather say them first.
Friction makes little fuzz balls - under the arms, where a bag rubs. It is normal, not a defect. [A fabric shaver, five minutes, gone.] The fabric library says which knits pill most honestly.
A knit loosens over a day's wear - elbows, waistband. [A cold wash and flat dry brings it back.] This is the fabric breathing, not failing.
Heat is the one true enemy - it shrinks and tires the fiber. Wash cold, dry flat, and a knit outlives three woven dresses.
A store that tells you the fabric's flaws first is a store that trusts you with the truth.