When finishing a knitting project, there are ends of yarn that stick out. "Knitpicking" is the act of removing these ends of yarn.
Knitpicking is given this name because it is tedious and time-consuming, and is something many knitters hate.
Knitpicking is done by taking a needlepoint needle or similar and running the excess yarn under the inside of the garment several times, then cutting off the excess.
finding faults in a garment that you want to buy, but can't buy for some reason. (most likely the price and the resulting sense of guilt)
The store manager wondered if she would ever stop knitpicking and finally decide if she wanted to buy the top or not.