My sister went to look at a higher mileage CLK270cdi and it was very poor (not saying this one will be) Watch out for poor power delivery (this seller said it was the air filter haha) mug she rang me i said walk away, also it was down on power badly, she said it felt like the turbo wasnt kicking in. EML was on big no no IMO also boot carpet missing etc. Just look out for the usual things. Its not that high for a car like that to be honest.
Full service history a must(pref mb)autobox oil/filter changes should have been carried out(2minimum at that mileage)brake fluid changes(every 2 years so 3 on a 2004)coolant i think every 4 years( though maybe wrong on that).Check the bodywork carefully as if it's a pre may 2004 car it won't be galvernised so check for signs of rust.When you test drive the car make sure all the electrics are working properly & that there are no unusual noises or lack of power delivery from the engine(the autobox changes should also be smooth both up & down the box)good luck