In the eighties and nineties the locksmith service was a very kept service, just like plumbing, and electricians. Locksmith companies were rare and professional. Many of them were passed down from father to son and so on. Many companies would have a few trained technicians on hand and most work would be done by the owners with the technicians being helpers. After the nineties there was an influx of foreign technicians in the field. These technicians came from all over the world, one way or another they learned the field and somehow or another made a career out of being locksmiths. Today in New York City alone there are probably hundreds of locksmith companies.and hundreds of locksmiths. Being a big city New York has become a transient city, people move in and out of apartments. Anytime someone moves in and out they usually change the cylinder on their apartment door lock. I always advise my clients to either change both locks or change one cylinder and install a deadbolt.