Bah, dagnabit you bastiches. How dare you create a scenario where I have to agree with something Fnfal says. 

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After you are DEAD.....you have no rights. New divers look at the DM for guidance.
BY THE BOOK.....BY THE BOOK... That is all I see on here. Where does common sense come into play? New divers need someone to look up to and get advice when needed. And if they have no one else with them that they know.....it should be the DM.
The DM is not your personal bodyguard or babysitter.
With solid planning, and free pre dive communication, a group of newly qualified divers
is quite capable of acting as it's own DM cooperative, building confidence to the relief
of all, as shared responsibility for each other, will lead to a quicker mastery through critique
OMG, knowone, what a coherent postI completely agree. However, in so many of the "green zone" forums newbies are advised to find a mentor to coach them in their skills development. For the land-locked, vacation diver this could be problematic. And while I am not here to criticize DMs for not being nannies, I would encourage them to think of themselves as the mentors many divers do not have. The less experienced divers will love you forever and refer their friends your way. If the experienced diver doesn't need your assistance, at least you checked and offered.
It's been many years since I guided, but I recall a bit of tension between helping a certified diver and extending your liability. I would always spend time during the trip to the site speaking with divers I didn't know. While it was framed as chit-chat, it was an opportunity to size up peoples comfort. Part of it was looking for non-verbal clues, like nervousness or difficulty setting up equipment, and part of it was casual conversation - "It sure is beautiful here, where do you normally dive?" type stuff. It was usually easy to get a perspective on a divers experience from these conversations. I considered this an opportunity to gain insight into which divers might benefit from advice or struggle a little with the dive.
An example of the tension would be encountering a diver certified for several years who took one or two dive trips annually, i.e. someone I would consider generally low experience. When a diver like this would do something I would advise against - for example putting on 22 lbs of weight when 8 - 12 lbs would most likely be sufficient the question was if / how to get involved. As a guide, and a host, I would usually suggest they might be more comfortable if they experimented with using less weight and I'd suggest a number that I thought might work. However, if they didn't act I would never pursue it further as appearing to push someone to take less weight could increase my liability if they had an uncontrolled ascent.
On the other hand, when I did my short bit of assistant instructing (DCS) I would be very clear and direct in my instructions and expectation. A clear challenge is that a new OW diver has just finished a relationship with their dive professional where they received direction and henceforth will likely get advice. This should be made abundantly clear to newly certified divers.
And, of course, I'm not talking about seeing someone do something clearly dangerous in which case I would take appropriate action.
I just think that the DM should have reached out to these people and tried to help.
I was going to ask you to define "help", but you gave me an idea with your subsequent post.
On a small boat, with a few divers, I could see the guide perhaps being able to make the rounds and look at everybody's gear and check the amount of weight they are using. I think a really motivated guide might, if he KNEW someone was brand new, make a specific point of checking such things and asking if the diver felt comfortable or needed any additional information to feel good about doing the dive. That's how someone earns his tips
But your comment about "you're own your own" and "cut the dive short" imply to me that you expect some kind of in-water assistance. Remember that the DM is a guide, and his responsibility, such as it is, is spread over all the divers in his group. He is not your buddy, unless you have specifically hired him to be that, in which case, his ONLY responsibility is guiding YOU. It is not the responsibility of the DM to monitor your gas, or to provide you with more gas with which to do the dive -- although I have seen guides do this in some places.
I have never dived with any dive op anywhere that did not either require you to provide a certification number, or require you to sign a form indicating that you had a certification number (unless you are an OW student, in which case your instructor is taking responsibility for you). By doing so, you have indicated that you are trained to dive, and although you may not be familiar with the specific conditions of that dive environment (which IS one of the things I think the DM is responsible for communicating) you should either be able to do the basic things involved in diving (such as assembling your equipment and providing yourself with the correct amount of weight) or you should know enough to ask for advice and assistance, if you require it.
I guess what I'm trying to get at is that I'm hearing a desire to abdicate some responsibility for your own diving and your own need to be proactive about the dive. If there are things about diving that you feel unsure or tentative about, it's probably a good idea to get some practice or even some additional instruction to shore up those weak spots, rather than to depend on a complete stranger (who has multiple other responsibilities) to fill in the holes.