Tough question.

Look for any service stickers under the hood, on the door frames, or wherever that might betray the odo.

In my area, I would expect the level of pitting on the headlamps to be fairly linear with mileage, and they may be too expensive to replace just to pull off a scam.

Look carefully for signs of accident damage. It may have low mileage because it spent time going the 'rebuildable' route.

Otherwise, enjoy! Great find!

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1986 300E 5-Speed 240k mi.