first check the overall condition of the board, no any sign to break two pieces. if someone used in wavy conditions or had very high weight you can see long cross wrinkle between the mast truck and the first foorstraps on top of the board.
after that push with your hand very hard the board under the foot pads. if you feel soft the skin of the board under the pads dont buy it, or calculate with repair costs. with simple injection easy to fix it, but if you heavy too, soon or later the board will be soft under your feet again.
check the board around the footstrap screws. if you see any crack, dont buy it. expensive and risky too to fix it. same with the mast truck.
check very carefully around the fin box. if any crack there, never buy it.
check the forums which fin works the best for that board and try to get that one.
hope its help. welcome in the "club", you will enjoy it for sure!