He should have verified it with some form of ID, either before or after he opened the door for you. This is a major point of liability for locksmiths . This is why most states require locksmiths to be licensed and bonded.
When one of my locksmiths go to a lockout I Make sure and remind them to get some sort of verification of address when they do a lockout.” We were taught to take a minute while getting our tools together or whatever and talk to the client, first by asking them outright for a picture ID, and if they didn’t have one on them, ask questions like, “How did this happen?” “You’re sure you don’t have your keys on you?” stuff like that. That second question may sound like a strange thing to ask, but trust me, on at least a couple of jobs the person actually did have their keys in a back pocket, or sitting on their car seat or something. We were also taught that if a job seemed suspicious, to just walk away, which I also did more than a couple of times.
Anyway, if a locksmith breaks into a house/business/car and the person who hired them is a crook and proceeds to rob the place blind, the locksmith would be liable as an accomplice, so it should be in his/her best interest to check up on these things