To identify a high-quality sweatshirt, cheque the fabric. It should feel soft, durable, and heavy, often made of cotton or a cotton-blend. Look for tight, even stitching, reinforced seams, and no loose threads. The fit should be comfortable without sagging or stretching. High-quality men's sweatsets often include well-finished details like ribbed cuffs and a sturdy neckline. Test the fabric's elasticity and ensure it doesn't pill easily. Lastly, consider reputable brands known for craftsmanship or read reviews to gauge long-term wearability.