All in all they are a very good luxury small two seater convertible. The main thing to make sure of is that the roof operates smoothly without any hesitations or clunks as it initially opens or closes. The bonnet leading edges are a stone chip magnet so have a good luck around there. Early models such as yours (and mine) had a batch of dodgy boot seals so check in the boot area on top of the wheel arches for evidence of damp. Obvious one this but check all electrics especially "option" electrics work properly. Early models again had a textured finish to the dash and doors which is a pig to keep clean, not a problem really but the idea is to not let it get into an overly grubby state, I know a few good ways to keep it pristine anyway.
Whats the spec by the way, I might be able to more specific then?
Correct, 1.8ltr, 4 cylinder supercharged, 163bhp. If you have not seen the spec yet?, as Colinb says airscarf is a must for all year open top use as is leather/heated seats (you cannot get heated seats w/out leather), most folks and this includes me would suggest auto as well. For my mind the lack of bi-xenon headlights and MB's OEM satnav (COMAND) should not be a reason to walk away but they are nice to have. Is it from a dealer? if so ask for a Tier 1 warranty + a full service + a good discount.