There was an article in Mercedes Enthusiast magazine (or whatever it's called) a couple of months ago. - I can try to dig it out.
Which A209 are you looking at; oil burner, or petrol? What options are you looking for?
I love distronic, so would recommend that if you've got the choice.
Check all the obvious things; does the roof go up and down consistently over a few runs? Do all the options work, that kind of thing.