S2000 Common problems:

1. Worn drive shafts - to test this, put the car on gear 4 when crusing at 50 km/hr and full throttle it. If you hear constant thumping, dependent on your rev it's most likely worn. Not too expensive to fix, and there are ways to prevent this from happening.
2. Worn roof, with holes, patches etc, rattling catchers - again, easy and not too expensive to fix.
3. Gearbox notchiness, make sure the shifting is more of a "pop into gear" than a "grind into gear" although s2k boxes are a bit "notchy".
4. Clutch master leaking - ensure the foot well under the pedal is dry as a bone and that when you step on the clutch it doesn't make unusual noises.
5. Ensure that the engine doesn't tick or rattle on idle under the bonnet - this could be the TCT which is also a common problem. Could be valve related too (adjustment)
6. Make sure your steering is straight and not tooo hard as the EPS system can get stupid sometimes.
7. Last but not least, ensure you don't have a check engine light lol

Other than that, the usual wear and tear stuff ie. Brakes/Pads/Rotors/Clutch/Tyres...

I sold my 99 Ap1 silver with red interior for 21,500 with the wheels/coilovers/intake + stock bits. It only had 105k on it. One will pop up eventually. Goodluck!

Peace.