1. Check the Deck and Hull Stiffness
If you're looking for a Laser sailboat for racing or recreational sailing it's best to start with a thorough check of the hull and deck stiffness. The best way to check is to press with your hands, if there are any soft spots they'll be easy to feel, ideally the hull should be uniform stiffness, it's common for older boats to develop soft spots. The good news is they can be fixed, but a boat with a soft spot probably won't be competitive for racing.
The best way to store a laser is on the dolly sitting on the gunwale supports, the second best way to store a laser is deck down on a flat surface off the ground. Check to see how and where the laser was stored. You'll be able to tell from feel and visual inspection if a hull has been stored poorly like on the ground or used as a garden planter.
2. Check The Mast Step
The Mast step test is critical when buying a boat, to do the test simply fill the mast step tube with water and let it sit. The water will leak into the hull pretty quickly if the mast step is bad. If water leaks out very slowly, the mast step will need repair but the step is likely still safe for sailing in the meantime. Check to see where the water level stops, sometimes there is just a pinhole leak in mast step tube. if there is a small hole in mast step tube this is a fairly easy repair but will require the installation of an inspection port near the mast step. If the water leaks all the way to the bottom of the mast step then the base of the step likely needs to be re-fiberglassed to the hull. This can be repaired but it's a pretty major repair on a Laser Sailboat. You should not sail a Laser with a mast step that leaks at the bottom of the step because it's likely the step will fail and rip a large hole in the deck making an even more timely and expensive repair. If there is only a pinhole leak in the mast step tube you can still sail the boat, it may take on some water especially in waves but the step is not likely to fail. You may also be able to repair this with some "marine tex" by filling in the pin hole with a stick, then sand down the imperfections.
Also check for wear inside the step, did the last owner let sand and dirt get into the step? If so it will literally look like someone used very low grit sand paper where the mast and mast step make contact. Extreme wear can effect the racing performance of the boat so a visual inspection of the step is just as important.
3. Visual Inspection
Give the hull a good visual inspection checking for hull/deck separation, cracks, chips, scratches and excess wear that might effect the boats performance, check all the fittings. Cosmetic issues such as chips and scratches are fairly easy to fix, they can generally be sanded and polished out, worst case it will need some gelcoat touch up. This can be done in an afternoon.
Inspect the spars and blades for damage especially the rivets and fittings. The spars (mast sections and boom) should be checked to see if they're straight. Bent spars will effect performance and may be more likely to fail while sailing. If you have a bent upper you can try to bend it the opposite way of the bend and see if it straightens out.
Check the sail, is it clean, white and crinkly or dirty, brown and soft like your t-shirt? A crisp sail is a good sign that it has some life in it, if the sail feels and looks like a rag, it is. A rag sail is fine for recreational sailing but won't hold up against new sails for racing.