It's often reported that Nikon won't repair gray-market gear, not will some other manufacturers. I've only bought one camera in a private sale and have purchased a lot of used gear since -- all from a well known used camera dealer that offers a 14-day no questions return and a six month warranty. In a private sale you never know the camera's history: dropped, water inside, sand inside, or any of the dozens of other bad things that can happen. Frequently if you pay too little you'd best set aside some cash to deal with unforeseen problems.
Bro, do NOT buy grey-market Nikon products in the US. Beginning 4 years ago, Nikon has changed the repair policy, 3rd party repair shops can not get Nikon parts.
Oliver
I'd personally feel nervous to buy a grey market product, even if there is some kind of warranty offered. This is because not only does Nikon refuse to repair grey market items, but they also try to make sure that nobody else can get parts to repair these items. My understanding is that a person who has a grey market item can find themselves with literally no way to get it repaired if something goes wrong. I'm inclined to believe this because I've read a lot of reports of even people even with "legitimate" Nikon equipment who couldn't get it repaired since Nikon had stopped manufacturing the parts, and while it was obviously older equipment I wouldn't say it was THAT old.
I'm seeing a lot of interesting and incorrect stuff here about grey market.
Grey Market only matters for warranty. Nikon will still repair them if damaged. When you're buying used, 99% of the time your purchase is out of warranty anyways - so grey market is not functionally any different than a USA model.
Source: Just had my Z9 + Z 400 TC 2.8 repaired by Nikon, both were purchased on eBay from MAPCamera (Japanese camera store) which would make them grey market.
I have never bought a single piece of Nikon gear new, always used from eBay or FredMiranda. Most of my equipment is grey market from Japan or India. Nikon still lets me register them, and still repairs them without issue.
While owning grey market items themselves is no worry, it is important to verify where you are getting them from. Some of the grey market sellers are very shady and have poor customer service. 6th Avenue Electronics on eBay comes to mind as one with terrible reviews.
Heck you can even read Nikon's own web page about grey market and see what is true and isn't:
Shop the latest mirrorless & DSLR cameras and NIKKOR lenses from the official Nikon eCommerce site. Explore our innovations and photo equipment!
www.nikonusa.com
I'd also wager that for anyone buying mainly used gear, they are inevitably going to obtain grey market no matter how thorough they are. Buying used always presents risks. I dropped my Z 400 TC 2.8 from shoulder height onto cement. Externally, you couldn't tell it was anything other than mint condition. I took it the next day and shot thousands of images in the Sax Zim Bog without issue. However, internally - it required $630+ of repairs to fix.
Imagine how many bodies and lenses get knocked around in travel, dropped, fall off tables, etc. and never get checked out because externally everything looks fine. Then the owner throws them on a for sale forum, it swaps hands, and nobody is the wiser.
Buying used is always a risk. If you're not interested in risk taking, buying new from Nikon directly is the only option.