When I first started to train I've worked with a few different PT's.
The first guy I worked with seemed to have a solid understanding of training, and a lot of ambition. He could never put it together though, he never had a plan for me, he just sorta came in and made me do whatever he was in the mood for. He was also fond of these dumb exercises that I hated and knew that carried no benefit, but he insisted on them. He also had a few problems outside of work, some days when we were supposed to train together, he wouldn't show up, no phone call, nothing. Overall I was very disatisfied with him, and wasn't the least bit sad when the gym fired him.
The second guy I worked with is Anthony Williams, a five time Canadian Bodybuilding Champion, who actually owns the gym I worked out at. I only did three sessions with him (he charged a lot), but I learned a lot and become more focused and intense with my training. I enjoyed working with him, he was an inspiration. When I wanted to quit he'd get right in my face and demand another rep, he pushed me beyond my comfort zone. I loved every minute of it.
The latest guy I worked with is also very good. He'd come to the gym with a plan, and he did his homework. His workouts were solid and challanging, I was sucking wind in 45 minutes. He also educated me on nutrition and other training related subjects. Great guy, I'll probably work with him again in January.
So I've had 2 good PT's and 1 bad PT, that doesn't seem too bad.