I’d make sure to either dump a couple of buckets of water or spray with a hose around both deck inspection plates, get them good and soaked. Then wipe them off and then have the seller open the inspection ports for you. Feel all around the fuel tank and see how much water you‘re touching. If there is a lot, you can almost guarantee that the fuel tank is sitting in wet foam, if the boat has been run in the ocean, that water is brackish. Doesn’t mean that the tank is necessarily “bad” but it does let you know that it’s wet and that those inspection ports are leaking and need attention……