Great cars - fuel economy aside, most jobs you can do yourself and loads of advice online, avoid ones where the air suspension has been swapped as the ride on air is fantastic, pretty easy to drive and great road presence. If you get one just expect to have a few issues like battery draining and electrical gremlins.
As you no doubt already know there are loads out there so it's a buyers market, just have your wits about you and go and see loads before you decide.
Few Pointers:
Check overheating,
Check air suspension works (will only operate with doors shut)
Check any/all switches work.
check all doors lock.unlock and indeed open! - remotes need to work or you will get stranded with the lock out message at some point.
Check sunroof works and doesn't leak
Check roof lining isnt sagging - usually starts in the back.
Check cruise buttons work on steering wheel.
Feel transmission tunnel by the dashboard for damp - Heater O rings are a dashboard out job
They are just a few things that can go wrong lol, but these cars have a huge following so they can't be that bad

And have a look at this guys website:
http://www.mez.co.uk/p38.htmlHope all that helps

Darren