Hi,
I've had my 2001 C320 for about two years now and apart from normal servicing (just a Maf replacement), she has been trouble free.
Things to check for would be:
1. Fsh, main dealer or good independent.
2. Rust, anywhere from the wheel arches down, especially the rear.
3. Make sure all the electronic items, air con works.
I average 20 mpg around town, to 30+ on a decent run.
Road tax is £270.
If you get a good one you'll find it comfy, effortless cruiser or a fast, surefooted Q car, to match whatever mood you're in.
Regards,
Chalpkin.