This 2018 C-Class is the W205-era saloon and most diesel examples use a 2.0-litre turbo diesel with a multi-speed automatic gearbox (9-speed on many cars). Look for evidence of regular automatic transmission servicing and note these diesel engines have DPFs and usually an AdBlue/NOx system on Euro6 cars — short urban use can cause DPF/EGR issues. Also be careful with cars that have been remapped; performance increases can shorten injector/turbo life and affect emissions equipment.

• DPF condition — any persistent warning lights, excessive smoke on acceleration, or evidence of forced regeneration after a short test drive
• AdBlue system operation and filler cap (if fitted) and unusual AdBlue consumption or warning messages
• Automatic gearbox behaviour and service history — smooth shifts, no hesitation or jerking when cold and check for any gearbox-related codes
• Turbo and injectors — listen for unusual whistle/grinding from turbo and check for smoke under load which can indicate injector/turbo wear
• Rear suspension bushings/subframe and underside corrosion — check for creaks, uneven tyre wear and corrosion at rear subframe mountings and trailing arms