A survey done by a reliable surveyor, with the surveyor marking all of the corners on the land itself is the only way you know what you are really buying.

If I am a buyer, I would also check the legal description provided by your Seller describing the land you are buying to make sure it describes the land that you THINK you are buying. Then send your surveyor out there to verify that the legal description accurately describes the land that you think you are buying. There are a few surveyors on the island, I believe. Just my opinion.