Here's what I can't understand. You book a trip with a dive op for X amount of dollars. Then if you want or need a DM, you get charged anywhere from $10 on up for that DM. Why doesn't the DM get that fee? If a DM takes four divers down at say $15 a head, he or she can make $60 for one-half day of work (2 tank dive). Do the DM's not get this money? If it goes to the dive op, why? I don't mind tipping but I'd rather pay the person doing the work.
There may have been some loosey-goosey terminology here, but there's a few ways this can work, and HOW it works depends on the boat and the area.
In many places there's a distinction between "boat crew" responsibilities and "DM responsibilities" though they are often the same people.
- boat crew manages "the boat" part of the trip, getting on/off, tieing in to wreck, etc
- DMs might handle dive briefings and such
Within the DM specific duties there can be further difference between "general DM duties" of dive briefing, checking divers in/out etc and "we have DMs in the water, follow 'em if you like" and "your own personal DM-guided dive."
Here in NJ, while the boat crew members tend to be DMs and Instructors, we aren't acting as DMs per se when we are crew. From a legal standpoint, NJ dive boats are a ride out to the wreck. We don't plan your dive, we don't lead your dive, we don't dive your dive.
The boats here aren't owned by or officially affiliated with dive shops, but most of our trips are chartered by shops. You book your spot through the shop that has that day's trip. We provide the boat, the captain, and the crew to run the boat. The shop provides DMs or Instructors as needed for leading the group and/or individual "rent-a-DMs" for folks who want their own DM with them. Works well for both the crew and the DMs. Crew handles the boat and related logistics without being distracted. The DMs/Instructors can focus on their divers and the dives without having to worry about the boat.
So the way it works out on the Gypsy Blood on any given charter is that you'll likely have a captain and three crew members running the boat and two DMs from the shop running the charter. With a load of 15-18 divers that better than a 3-1 ratio, and ensures that you will get as much (or as little) attention as you need from great people dedicated to making sure you have a fun, safe trip.
As to how the various DMs are compensated, that depends on their arrangement with the specific shop.