As a seller, you can't know everything about a boat, even if you owned it for years. Electrolysis in aluminum, for example, is very hard to pick out, but you can tell how long it's been around, so even in that case....
Let's say you sell a wooden boat. You can't tell that the keel is spongy because you have such thick marine paint over it. You can't tell. That doesn't come back after a year when they find out that this sponginess occurred over the course of maybe two years prior. That doesn't come back to the seller.