Why does it have to be one or the other? Your main point is that one requires instruction to attain the correct form. That can be achieved by reading the book and properly following it, or seeing a competent trainer, or both.
There are some good trainers who can help, and there are certainly many who are worse than useless.
As for the book, it has hundreds of pages explaining in great technical detail exactly how each exercise is to be performed and some useful photos are also included. There's no reason why you can't get the form down properly using the instructions in the book, and maybe even have a friend record your form so you can check it against the photos.
I've read the book many times, looked at reputable youtube videos, had people with perfect form try to correct mine and still have trouble understanding how to do the lifts perfectly. My brain just turns off during the workout and takes a while to come back. Starting Strength's 30 pages per lift are also overwhelming. I really only need a checklist of 30 things per lift and have to figure out which to emphasize for my crap posture, knees out, chest up, etc.
My numbers should be better, 2.7 years, 185 BW, 400 lb deadlift, 275 bench, 275x5 squat, 150 OHP. All thanks to crappy form, not understanding how to do the exercise properly. People with hunchback posture have a lot more to think about than those with good posture. I got to 375x5 deadlift within 1.5 years. But my form was already crap at 245 and I had no idea because I only checked with video at 225. Also filmed myself and couldn't tell what I was doing wrong, looked ok as far as I could tell at the time. But it was wrong. My idea of how to deadlift/squat/OHP was fundamentally wrong at 1.5 year mark. Bench needed major corrections.
You might be doing it wrong too, you can get away with it for a long time.
A trainer at some globo gym like Planet Fitness, Bally etc. won't promise correct form for 300 lb deadlifters, even if they pull 500 lb themselves. They're just there to make total novices feel comfortable.
If you want proper training you need to find a freeweight focused place like a powerlifting gym, maybe crossfit and pay whatever obnoxious price they charge for personal attention. Train a few months there to get started. Or hope you're not as dumb as me and rely on youtube and books.
There are some good trainers who can help, and there are certainly many who are worse than useless.
As for the book, it has hundreds of pages explaining in great technical detail exactly how each exercise is to be performed and some useful photos are also included. There's no reason why you can't get the form down properly using the instructions in the book, and maybe even have a friend record your form so you can check it against the photos.