I wonder if part of the problem here is expecting this to be a (free!) service
Anytime I'm going to do something like this, I've asked in advance, in the same respectful tone I'd use asking anyone a favor they are well within their rights to decline. And, if they said they weren't able to help me out, for whatever reason, I'd be OK with that, and leave on good terms.
In my experience almost every marina (or other business) I've approached this way will do what they can to help out. Marinas
especially tend to go out of their way. I can't count the times I've been offered the dockmaster's personal vehicle to run an errand. I'd only accept an offer like that if there were no other way, but that's the sort of thing most will do.
But demanding customers with an attitude of entitlement get a very different reception
. I'm NOT saying Charlie is one of those. It could be there are just enough of that type there that the marina has to take a hard line with everyone.