I had a fortunate experience with lessons, long ago. I have related the story, perhaps more than once on this forum.
It is however on topic and worth repeating.
In the middle 80s I was regularly winning a local B tournament and doing well in the small fry ring games. My theory was that I could learn by investing my winnings by playing a Road Player cheap. He seemed to have a weekly circuit around the Seattle Tacoma area and I was shooting $20 at him on a weekly basis. At first just thinking if I lasted longer I was getting better. It didn't take long for me to figure out that I lasted as long as he was in the mood for, usually around an hour. So realizing the folly of my theory, I proposed lessons at $20/hrs. I was thinking of learning one pocket theory and shots, as that was his game that the locals champions couldn't touch.
His answer surprised me in a good way. It was, "I will give you lessons on one condition." Okay "what's that", was my inquiry. "We go back to Basics", was his reply. It tipped me that he really knew how to give lessons, so "Okay" was easy. Then he added a stipulation...No gambling while taking lessons. I needed to focus on rebuilding from the ground up.
One hour a week for 6 weeks before he went south for the season. The first lesson only addressed the stance and how to get into it. He gave me some simple drills and the prescription was spend an hour a day locking in what he showed me. The next week we moved on to the delivery of the cue. Each lesson allowed the one week of practice to break old habits.
Backward Jan was the name I knew him by. He got that handle because he turned his baseball cap backwards when he was in action.
My experience would lead me to advice of, avoid the one lesson miracle improvements advertisement. Pretty much avoid anyone that doesn't want to start with The Basics. So many B players think (as I did) that they are ready for advanced lessons. The investment of time and confidence in the coaching can pay dividends.
If and when a coach or instructor is chosen, show them respect. Take the course without running it by others to see "WHAT THEY THINK". Give their method a chance without poluting it with second guessing by the Peanut gallery.
And if you encounter or know Backward Jan.....ask for lessons.