It is up to the manufacturer to take the time necessary to assure that the product that leaves the factory is of the highest quality. We also tend to reject a fair amount of raw material. This is a costly process that could be skipped. Telltale signs of a cheap or poorly made product, if you will. The wire should be shiny and smooth from end to end.
Consistency is important.
Eric Johnson once noticed an intonation problem with the .018 gauge strings he was receiving from us. It was discovered that the wire size was slightly inconsistent from end to end. This was an extremely minor inconsistency in the wire, which an ear like Eric's was able to pick up. Poorly made product would have an inconsistent look to the wrapping or tarnish or spots. A spotty wire may not necessarily have an effect on the tone, however a badly tarnished string is a sign that is has been subjected to poor storage conditions.