I didn't research the shops before going to St Thomas and was limited by family activities from adequately investigating the shops before diving. My first dive was a drift dive to Thatch Cay with Coki Beach Dive Club. I can't say enough good things about them!
For the second and third I relied on the recommendation of Marriott's Frenchman's Cove to go with Underwater Safari's. While many aspects of the trip were well-handled, the nine other divers were all from the cruise ships and, although I told the dm I was alone and a relatively new diver, I was not assigned a buddy. The one dm trucked ahead and assigned one of the paying divers who had some rescue experience to bring up the rear. 15 minutes into the first dive, at 55 feet, the dm turned around and signaled stop. I looked up and saw a diver near the surface with her companion following. The dm told the group to stay and went up. After about 8 minutes he returned and signaled for us to surface, which we did, somewhat too close to Buck Island. He shouted that someone had shot to the surface, that we needed to return to the boat to take her in for medical care, and that we should swim underwater to the boat. After a hard 5 minute swim, we made the boat. The victim was standing by herself with no one attending her. The word was that she had recently run a marathon and suddenly was unable to breathe underwater. When she surfaced and was picked up by the boat, she was coughing up blood. Only after we got underway did one of the crew go over to get her, have her sit down and administered oxygen. We returned to shore and she was taken off in a wheelchair.
The shop then offered that they would take us out again to the Navy barges. This was a pleasant and somewhat interesting dive, but we surfaced after 35 minutes. In retrospect, I still should have asked for a partial refund. The first dive was a complete wash, and the second was short. But the $ issue was secondary to the fact that there were too many divers for one dm, and that my own safety was jeopardized by the failure to assign buddies. I can't imagine what it would have been like if they had had their full quota of 30 - 40 divers.
Anyway, I learned a lesson - never, never dive with a cruise ship dive shop. And avoid Underwater Safaris.