Look at other garment details. Collars, pockets, and zippers should be smoothly applied. Look at buttonholes. Note trims as well. When shopping on the web or from catalogues it is not possible to actually examine and handle the fabric.
Some companies provide very complete descriptions.
Look for specific mention of reinforced seams, taped shoulders, double stitching, or other references to quality construction. These are cues for the shopper. How well a garment is made affects both durability as well as appearance over the life of the garment. Styling Style features and other detailing of knit shirts may influence your choice. Consider styling features and how they relate to the wearer's needs when selecting knit shirts.