Fair price for low mileage R171?

Hello community, at the moment I’m driving a C320 Limosine, but now I want to fulfill the long-runned convertible dream. A neighbor of a friend wants to sell your vehicle because she hardly uses it. The lady is already over 70 and has only gone shopping with the SLK. Highway has never seen it! Is this possibly a problem, because the vehicle has never been “taken in” properly? Due to the extremely low mileage you will not find any comparable vehicles at that age. The data: SLK 200 Compressor Approval: 11.2004 KM-Stand: 9,500 km (!!!) 1st hand garage car Obsidianblack metallic leather: Nappa tobacco brown 10 spokes 17″ with mixed tyres (245/225) Parktronic Asher package Airscarf 5 gear automatic exterior mirror li. u. re. electr. foldable Command APS with DVD Navi air conditioning (no automatic) battery with larger capacity (one year old) front for roof support system wood version Vavona Seat heating Windshield washing system heated Light package Interior Infrared FB for Variodach NP 46.666 incl. VAT. The condition is good but not excellent. Is probably more often the dog on the passenger seat. The rims on the passenger side are messed with by the curb driving. Flasher glasses on mirrors have cracks. Two small paint damage (must be able to fix for 300,-). Was only once at MB for checkbook care, otherwise oil change etc. in free workshop. The wooden parts fell m The Tabacco leather looks a bit “wolky” (not even brown), but the lady always said that was so. Is that so? So: What is such a car worth? Or better take a vehicle that is 2 years younger and has e.g. 50 thousand km. How much is 1 year or 10,000 km less in the price? Is there a fist formula? Alternatively, someone in the area sells his 350er: 2004, 73,000 km, black metallic, navigation command , radio/CD changer, climate, leather black, 7-speed automatic with Tiptronic, 2nd hand, 17-inch alu, Karman HiFi system. To cost 20,800. I have not yet been able to contact the seller.