I purchased a suspiciously inexpensive Nikon MBD16 vertical battery grip from an eBay seller that claimed it was authentic.
When I received it, the box and even the papers had some convincing Nikon branding on it. It even had a fake warranty card in it!
However, what made me suspicious is that the battery grip did not have rubber coated front and rear dials like my MBD18 grip (for my D850). Also, the AF joystick on the grip had a "clicky" imprecise feel that I've found to be present on the clone grips sold under the Meike, Vello, DCOplus, etc brand names. What ended up making me realize it was fake however was that the serial number is "2000082", which is not a valid serial number - also if you look at the auctions on ebay, you'll notice that ALL of these counterfeit suspiciously cheap battery grips have the same serial number regardless of which seller it is!! Unfortunately eBay is not doing a good job filtering out these fakes, so hopefully this post helps people avoid my mistake. Pics below - as you can see the packaging is very convincing.