There isn’t a completely foolproof test, but a few checks can help:

• Shutter count: still useful as a starting point. It tells you how much the shutter has been used, even if it’s not absolute proof of the camera’s full history.
• First-power-on behavior: many Nikon bodies show an initial language-selection prompt the very first time they are turned on. If that prompt appears, it’s a good sign the camera hasn’t been previously set up.
• Receipt / proof of purchase: if buying from a private seller, ask for the original receipt. Stores often include the serial number, which helps verify purchase date.
• Serial number / warranty check: if buying from or through a dealer, Nikon support may be able to tell you whether that serial number has already been registered for warranty.
• Physical inspection: check the mirror box and general wear. A body can look clean externally, but signs of use may still appear in high-contact areas.

So: use shutter count plus first-start setup behavior, serial/receipt checks, and a careful inspection. Together they give a reasonable picture, even if no single method is definitive.