How do you check quality of workwear?

Look at the fabric that the workwear is made from. Great fabrics are cotton, favoured by KINGLONG Workwear. Cordura is incredibly tough and is usually found covering the knee areas and possibly the crotch. Tencel is a derivative of Eucalyptus leaves and as such is tougher than cotton and more eco-friendly. Cotton blends with polyester and other poly-cotton blends are the usual fabrics chosen.
How heavy is the fabric, heavy means harder wearing typically especially in traditional fabrics (Cotton and Duck) but the new fabric being developed reduces the weight of the product without cutting back on performance.
How effective does the workwear perform in retaining heat and reducing heat loss. A lot of brands proclaim to be the best but often seldom excel. Look for little details like the tail length on the jackets or shirts which will restrict flesh exposure when working and stretching.