The price of a Cat 336D is primarily driven by its engine health, hydraulic performance, and operating hours. You must verify the Cat C9 ACERT engine condition, ensuring it meets emission standards (Tier 3/Stage IIIA). Check the hydraulic pump pressure and cycle times for the boom and bucket; any lag significantly devalues the machine. Additionally, inspect the undercarriage wear percentage—if the tracks, rollers, or idlers are at more than 70% wear, you should negotiate a price reduction to cover imminent replacement costs.