I've been seeing one for most of my life. Not the same one, but continue to go when my back is out of whack. He certainly helped me when they thought my lung was collapsed ---- it was my back out of alignment!
It all depends on what the problem is with your back. Sometimes it takes several visits, other times it just takes one.
If you feel uncomfortable with the recommendation by all means get a second opinion, or even a third.
Good luck.