If it isn't, nothing will cover it up. Cleaning out the boat can be as important as cleaning up the boat. Baggies full of little unknown bits and pieces, most of which are probably useless, aren't going to impress a buyer. If it's important stuff, inherently important to some piece of gear, put it in a labeled container. If it's junk, treat it accordingly. .
Buyers expect to do some cleaning, but they also look for some signs that the seller was a sailor.
Tidy up and organize lockers and storage spaces. Place gear in appropriate places and do your best to de-clutter everything. It piques the buyers imagination, and the stuff might even look good. It's often said that furnished houses sell better than ones stripped to the bones. Boats are not different in this regard.