In a lifetime of buying boats, I've never even considered sharing a survey with another buyer. A survey is a personal contract of private information, to be used by the purchaser to determine a fair price. I won't even show it to the seller. It is MINE and therefore I am happy to pay for it.
As for the bottom cleaning, it behooves the seller to have a boat with a clean bottom for the sea trial, but if he doesn't care then you have to decide what the odds are that you'll buy the boat and if you do, will you want to haul twice? I usually do an in water survey of a vessel myself to see if it is as advertised, anyway. If I'm satisfied, then I will have the boat hauled and surveyed by someone else, to insure my personal desire for the boat won't influence the survey.
As for the bottom cleaning, it behooves the seller to have a boat with a clean bottom for the sea trial, but if he doesn't care then you have to decide what the odds are that you'll buy the boat and if you do, will you want to haul twice? I usually do an in water survey of a vessel myself to see if it is as advertised, anyway. If I'm satisfied, then I will have the boat hauled and surveyed by someone else, to insure my personal desire for the boat won't influence the survey.