This is the W177 A‑Class hatchback in diesel/automatic spec — most 2021 diesels use a 7‑speed dual‑clutch gearbox (7G‑DCT) and Euro6 diesel hardware, so you’ll commonly see DPF and EGR systems and some cars use AdBlue/SCR. The MBUX infotainment and premium trim lift the cabin but repairs and dealer servicing cost more than mainstream brands; competent independent Mercedes specialists are a cheaper option for routine work.

• DPF behaviour — ask for evidence of successful regenerations and check for frequent warning lights, heavy soot smoke or recent forced-regens (short-trip city use clogs DPF).
• Dual‑clutch gearbox shifts — test for smooth low‑speed take‑offs, no judder or hesitation and confirm DCT service/recall history; mechatronic faults are costly.
• EGR and turbo carbon build‑up — look for sluggish response, black smoke under acceleration or rattles from the turbo and check boost pressure recovery.
• AdBlue system (if fitted) — filler cap, sensor lights and any stored faults; a failed injector or sensor can produce warning lights and limp mode.
• General underside and suspension — check for oil leaks around the engine/gearbox, and inspect rear suspension bushes/tyre wear (torque from diesel can cause uneven wear).