BLUEMOMENT

Are you planning anything to help owners whose boats are poorly maintained and under equipped?

I don't think that's likely. They will surely equip them to the level they need for certification.
Whilst not someone who owns a charter boat, the margins will be quite narrow I guess, so they'll be keeping expenditure well under control. This explains poor standards of maintenance - better for the profit margin to cobble a job yourself for free, than get a yard to do the work and get last weeks profit gobbled up.
Not offering this as some form of justification before anyone starts shouting at me!

How can you wield some power? "Lets all join up and not charter from these people who don't maintain their boats?"

That would be so hard to coordinate and even more difficult to drive. Don't you just go to the yacht charter association and report a member and then get them to deal with it? You've always had that right.

Did you get a sizeable refund?

I would have thought that the bad publicity from this sort of thing being made widely known would be more effective. A dedicated area of a well visited forum where people could post experiences - good and bad - would be useful both for prospective charterers and the better chartees.