As we use the word "pro", what are most referring to. The first guy I took lessons from was the pro at a driving range and had spent the better part of his life trying to avoid getting a "real job". The second was a kid that had played in college and worked for a golf store as their in store pro. The third instructor was a single pro at a local golf course. They have a very nice indoor facility. Lastly is a pro that runs a complete golf school in two locations with at least 10 other "pros' working for him.
Anyway, my only way to relate is my experience in coaching hitting in baseball. Never played a lick past high school, but I started coaching hitting as a way to make extra money. I felt I owed it to kids so I studied everything I got my hands on, and in the end became quite good. As I made the rounds and watched others coach young people to hit, I saw and heard terrible advice/intruction. People seeking knowledge have a belief that the more they pay for it the better it is Sounds like a fine assumption, but by no means 100%
so back to your post, one lesson is not a good judgement for the most part BUT if you did not have the communication with you pro and expect a "breakdown" then maybe one time is enough. As others have said, ask and interview til you are satisfied. If the pro doesnt have time for this then you dont need him. A couple of thoughts,
MY best golf instructor was the lone guy at the golf club, very calming and explained the reasoning behind everything we were trying to accomplish. I left him because he was absent minded and often forgot or double scheduled my time slot.
Secondly, as a hitting coach, the students make you. I could probably improve anyone's swing, but no one can turn a Bill Gates into an Albert Pujols...
Good lucj