I recently attended a concert in Austin, Texas, in which a 1666 Stradivarius violin was played by violinist Soojin Han.  In a pre-concert talk, she stated that she tried three different Stradivarius instruments all made from the same tree.  She said they all sounded different, but she selected the one that fit her best and had the sound she liked.   Stradivari would have had to evaluate the instruments by playing them or perhaps he had other means to tune them by ear.   Modern techniques might mechanically vibrate the violin and look at a frequency spectrum recorded by microphones to determine what makes the violin most pleasing to the ear.  I would guess that such methods might lead to more consistency than Stradivari himself was able to accomplish.  

For hundreds of thousands of years, quality has been carried by craftsmen. Craftsmen have quality as their mother tongue. They have studied for a long time, and know their profession "on the tip of their fingers". It was Taylor, by entrusting the work to workers with limited competence, who invented the quality controller position. And that’s when the situation got worse.