Looking to buy my first Copan

Here is a good start…
Daihatsu Copen Buyers Guide

 

-No cam belt, they are chain driven. If oil changed often they should last quite a while, and will rattle when worn.
-Rust spots tend to be sills, particularly near the front wheel, and rear arches, check under boot carpet, you can lift it up to access toolkit and roof ecu area. Even if you don't find rust, don't be surprised if you find body filler or other stuff hiding it later down the road.
-Check roof works.
-Look for wet under and behind seats, old car = old rubber seals (which the Copen has a lot of being a convertible) and that can lead to leaks.
-On test drive, listen for engine rattles and noisy turbo (some noise is normal but it shouldn't be excessively loud or squealing), should feel a noticeable increase in torque at around 3k-4.5k if turbo is working well (2.5k and below there wont be so much which is normal as its less than 1L). If you really want/allowed to, you can inspect the exterior intercooler piping for excessive oil build-up/leaks and remove air filter and look inside the pipes for excessive oil build-up. A light film of oil can be normal for turbocharged engines, but if its very oily or even dripping out, that could be a sign of a serious problem.
-Rattles from roof are normal.

The rest is just what you'd check on any other car.

Aside from rust, they are generally reliable so long as you follow the maintenance schedule and let it warm up before beating on it (and perhaps check valve clearances every so often...)