About 20 years ago I had a truly bad DM while diving with an operator with a large number of boats. Our first dive was on Palancar caves, and we dived it as a wall dive. We went over the edge, swam along the outside of the coral, and then headed to the surface, never even glancing into the labyrinthine structure of the site. I asked him why, and he said some of the divers in the group were not good enough to handle it. That was B.S. Everyone was plenty good enough.
The second dive was at Las Palmas. He said he wanted to check the current first, and he went into the water to do that. Then we descended, and as we dropped, I could see by the particles floating by we were going the wrong way. When we started along the reef, there was no doubt about it--we were diving into the current. We went on for a while, and finally when another group was coming toward us, he had to admit his error and turn us around. We were done with the reef in minutes, and we spent the rest of the dive drifting over nothing of interest.
I sent an email to the shop to complain, and I got an interesting reply. I was told the DM we had was not one of their regular DMs. He was a substitute taken from a pool of freelance DMs that hang around hoping for a last minute job. (I got a refund, BTW.)