Most slip contracts, even short ones, include a statement avowing you will purchase fuel only from the marina fuel dock.
While I don't like the idea of "price gouging" , I do have to agree with some earlier statements here that running a marina and providing services, insurance, etc., at the actual lake site, is an expensive proposition. With all the private marinas being sold for condos, I think we ought to just buck up and support our support groups.
Just think of how difficult it is to be there, ready for customers, during all the slow times!
John