They send out someone in an unmarked van who doesn't have a locksmith license (at least in CA these are a legal requirement and they are required to show it to you). When you ask to see it they tell you they keep it at the office for "safety". That was the extent of my personal experience.

I've read that if you let them work on your property, they will claim your bog-standard lock is unpickable, and charge you an exorbitant amount to drill it (destroying the lock) and replace it.

Almost everyone who calls a locksmith is in a hurry, dealing with something unfamiliar, so people are susceptible to this.