There are a few key ways to determine the quality of stainless steel. One is to look at the grade mark on the metal. The higher the grade number, the better the quality of the stainless steel. Another key way to tell is by looking at the finish of the metal. High-quality stainless steel will have a smooth, glossy finish, while a lower-quality piece will have a more matte finish. Finally, you can also test the metal's resistance to corrosion by scratching it with a sharp object. High-quality stainless steel will resist corrosion and show no evidence of damage, while a low-quality piece will corrode and show damage from scratch.