I agree with everyone. 3500 for a C-Class with 200K is a little rich. What part of the world are you ? I got my 95 C280 for 1200. Rust free and very clean inside and out, with 140K on the clock. Now luck for me I payed so little because, A few months after I got her it needed a head gasket. And when I was doing gasket I found that the wiring harness was shot. Still can't belive Mercedes would not do anything for any of us that had that problem. Wires fell apart in my hand. I did the gasket and made my own wiring harness, so it did not cost me a arm and a leg. But I have to say I love the car and would get another one. It handles well good on gas and is good in snow. And is a rocket ship compered to my SD...LOL
I would find out if buddy did any head work and look at wires. Easy way to check is to look at injectors wires. If there split and has coating falling off offer the guy 1500. I think you could find one for less with less Miles. I can find you a few in your area if you want. I spend my days looking for rigs to buy and sell. Would only take a sec to find a better one for yah.

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83 300TD Sable 402K " Work Truck "
81 300SD Gray 240K " Loner Car "
04 E320 Blue 90K " My Winter rig "
07 BMW X5 4.4 118K " My Summer rig"
04 Jetta TDI Wagon 168K " Wifes "
08 Toyota FJ 109K " Wifes winter rig "
04 Jetta TDI 120K " Daughters Car "