I did my own survey, theirs certain things you need to look for on the transom... Check all the bolts on the bracket,for any signs of bleeding or stains coming from them. There should be a a 4X4 piece of wood glassed into the transom up top. Look at the vertical pieces of wood that connect to it, are there any cracks in it? If the boat has no bottom paint then it usually means it never sat in the water. Which is a plus. Check the hoses that connect the scuppers to the deck drains, mine was all rotted out and I replaced each through hull. Last. Jump up and down on the engines, see if they flex at all.
If all,this checks out then u have a good hull. I love mine , I've had makos , whalers, sea crafts, but so far I'm in love with the room that the gulfstream provides. It's an awesome boat.
Good luck.