The black paint wears off where your thumb actually rests
You can always tell when someone has tried to age a camera on purpose with fine sandpaper: they rub the top plate corners evenly, as if the camera had been tumbled in a bag of gravel. Real wear on an old brass body is lopsided and specific. It shows up behind the advance lever where the knuckle of your right thumb pushes through the last ten degrees of the stroke, and on the bottom edge of the back door where the heel of your palm steadies the camera at 1/30.
The body I carry had most of its paint when I bought it four years ago, except for a bright crescent around the strap lug on the left side. The previous owner must have worn it slung across his right shoulder with the lens pointing inward, the exact opposite of how I carry mine. Over the last two years a second brass patch has slowly appeared on the right lug to match it.
None of that makes a sharper negative, of course. But when you pick up the same piece of metal every weekend, the worn spots become tactile landmarks. You know your thumb is on the shutter dial and not the ISO collar without taking your eye off the viewfinder.