The most common thing locksmiths are known for is making copies of keys. It is for this reason that key duplication is offered at locations other than lock shops such as hardware stores. It is not that simple!
Certainly a copied key that doesn’t work is obvious. What is not so obvious is how keys improperly cut might work initially but over time improperly wear a lock cylinder (or the key) so that a key will not operate the lock at some future time.
Key duplication accuracy starts with a high quality key blank (the metal form which is cut to match a key or lock cylinder) that meets the manufacturer’s original specifications. It continues with the quality and routine maintenance of the equipment that duplicates the key blanks.