fisherdvm:
It is only their job to check and make sure you have a C card. Beyond that, they are doing more than it is required.....
Actually I have the guides do the cert check/waiver.
As a captain I'm responsible (legally) for whatever happens from when we leave the dock until we return, even if what happens is totally beyond my control. My job (in addition to handling the boat) includes surface watch, alerting the dm/guide to potential problems, assisting with entry/exits, final predive checks and general monitoring of the entire trip.
The things that get me worried about specific people are:
1. Too much gear (especially if it's brand new). People seem to feel that owning gear somehow transforms them into a better diver...
2. Too many cards: Especially that guy whose got the DM or above. 90% of these people don't work as DM, they just got the card to show it to people.
3. People who have a specific thing that they don't want to see. Invariably the first thing that happens is that these people see the object of their terror (ok lets be real: sharks or eels). I've even had a person tell me they didn't want to see any FISH (yea like that's not a panic attack waiting to happen).
4. People who start the trip by telling me they always get sea-sick.
5. Old guys who talk too much story. Anyone who tells me that they've been diving since 'before I was born'. Interestingly enough this seems to be a male-only phenomena, older women divers rarely pull this crap.
6. People who start by telling me that they haven't been diving in 1 + X years.
7. Lawyers. Sorry all, but these people still scare the crap out of me.
8. Anyone under the age of 14.
In general I look around and see who acts comfortable and who does not. I chat with people (I'm the friendly kind of captain). I pass any observations on to the guide, often in sign form.