I'd give it a light sanding and wipe it with denatured alcohol. instead. It's safer.
Checking for a straight, fair and square hull with no twists needs tools, but very simple ones. A tape measure, level and a pair of straight sticks will let you do it by eye. Look in the Shop Tips for how to do it. They should have an explanation with pictures and videos. If you still have questions, come back here.
Tap the wood (everywhere) and listen for sudden changes in sound that may indicate rot. Look for black stains that may indicate water instrusion and rot. Look everywhere that you can, use mirrors, strong lights, a video camera on a stick, etc. The place you don't inspect is where the rot will be.
Look carefully at all the joints. Be on the lookout for sloppy fillets, glass tape that has pulled away from the putty, bubbles and poorly wet-out glass (glass that is white instead of clear).
Make sure that the deck is securely seated on the sheer clamps, bulkheads and deckbeam. If it's nailed, make sure that all the nails are completely in the sheer clamps and not poking through the sides. No open holes in the sheer clamps. Any missed nail holes should have been filled with epoxy/woodflour putty.
The deck should be securely sealed to the hull by the glue. If there are any openings, check them for water intrusion.
Get the boat out in direct sunlight and look inside with a mirror or camera, looking for sunlight coming through unplugged holes. Note that a well-made joint can be translucent, that's not a problem. What you're looking for are cracks and holes that need to be sealed. if you find any, check for water intrusion.
If you do find any problems but still like the boat, keep in mind that this style of construction makes fixing problems reasonable. You can still get the boat, but you may want to adjust your offer to reflect the extra time and materials you'll need.
Good luck,
Laszlo