You tell them where you're going, what you expect the depth, visibility, current, surge, temperature, seas, and other variable conditions to expect. You tell them on days that you expect to be crappy that novice divers may be unhappy. You watch them gear up and see how comfortable they are with their equipment. You give an excellent briefing of what to expect in the water, how you expect them to react in certain situations, and how to get back on the boat, for any fool can fall off a boat, but it takes a certain special skill to get back on one, and every boat is different. You listen carefully to the divers questions and statements, for the diver will always tell you if they are nervous, but maybe not in so many words. You show interest in the diver and ask where they've dived before and where their last vacation was and how many dives they have.
All of these things are done to evaluate the diver before you ever get underway. They are effective to the experienced charter boat captain. The AOW card is a crutch for a charter operator that proves that a diver has completed 9 dives with an instructor. Maybe not such a big deal.
Too many charter captains show up to the boat in the morning (at least in the keys) all hung over or puffed with ego. I don't know why, they have brand new 50 ton licenses that they just bought from Sea School. Anyway, they check the oil, fire up, give a 4 minute briefing of where the water and lifejackets are and how not to plug the head, and then tell the customers that the wheelhouse is off limits. They call a roll call and have the mate/dive guide/deckhand throw lines. This is no way to learn the experience of your divers. The Coast Guard requires that inspected vessels demonstrate the donning of a life jacket by a crewmember prior to getting underway, as well as an abandon ship drill within 24 hours of getting underway. How many times have you seen a charter captain follow either of those rules.....