Sure it works that way. An experienced instr or DM can very often spot a problem as they walk down the dock to the boat.
You can't look at a diver and say; They'll be trouble, unless you've evolved telepathy and we haven't.
Have trouble managing to carry your gear to the boat,
Ever run into a disabled person? I know several people who have reduced arm strength and couldn't carry their gear well.
Oh, I get it. New diver can't buy equipment, and experienced divers will never be caught without theirs. So easy. I guess you've never heard of things like theft, airlines losing bags, or just owning the wrong gear for the climate and having to rent?
asking questions like"how much lead do you think I need" all all giveaways to inexperienced divers who probably need to be watched carefully.
What about a diver from the Pacific NW who has only used a drysuit, even in OW certification? Think they may ask how much they'll need, never having been anywhere warm?
My point is that DMs are not dive gods, though in my experience many (not all) like to think they are.
The DM absolutely is what you may call scuba police. If the DM feels through either direct or indirect observation that a diver on the boat may be a liability to him/herself or others diving off that boat the DM has an absolute obligation to do something about it. Rather lose a customer than have a dead one on the boat
No, they don't. They can suggest, recommend and offer, but cannot order, direct or require. DMs are not the scuba police; and it is the mentality that they are that leads to the unskilled divers that continue to proliferate.
Second, a DM is not there as a supervisor or boss, they are a guide. Nothing more.
Waiver does not prevent having to explain to authorities why you have a dead diver on board. I can just see it, "yes officer I observed that the deceased had 30lbs of lead on him,when everyone else wore only as much 12lbs or less, yes officer he is smaller than most others on board, and I observed he needed assistance assembling his regulator to his tank,but I knew he signed a waiver so I did not do anything to make our charter any safer." If the dive pro did not take action on what he observed and acted differently than what a reasonably prudent dive pro would do , then he indeed is negligent and THAT is not signed away on any type of waiver.
And if the passenger insists that he can't get down without that 30 pounds, or that he knows what he's doing? Or reminds the DM that they're not responsible for them?
DMs, and no one in scuba, has a requirement to act, unless the indication is clear danger- in that case, they need to be denied the dive. Second, even if they felt there may be a problem and let them dive, that would be simple (not gross) negligence. EVERY waiver I've signed releases a crew/boat/operation from being responsible for me- to include negligence. Just how many sucessful suits have there been against these waivers? Zero? Thought so.
It's this sort of mentality that leads to the unskilled, dangerous divers. The sort that remember the last time, how the DM guided them around, assembled their gear, and treated them like sheep. We get these divers because they get reliant on DM/instructors to do everything for them, and all they have to do is follow like good little sheep.
Until we break DMs of the habit of treating certified divers like one-size-fits-all sheep, you'll continue to see this problem. I know it's not popular, and the DMs will fight to defend their little bit of turf, but it is the truth.
I'm new here so you can take this with a grain of salt, but I think if I owned an organization like Rainbow Reef, and I had some divers on board one of my boats, and they came across to me and my experienced guides as "unskilled", I could see making the call of "You need to either dive with one of our guides, or not dive from our boat." Because you know as soon as that "unskilled" diver has an incident with a negative outcome, who do you think he is going to sue and come after legally.
That's why you give them the choice. But to require it without justification, and en-mass is absolute ridiculousness.