The only Nikon cameras I've ever sold were for friends or dead ones sold for parts. I still have my very first real camera, a Nikon FE2 bought in 1984. It died in about 1999, but I keep it for sentimental reasons. I still have a couple of FM2ns and a few Nikon lenses.
I inherited my first Leica in 1998, an M3 which I've carried almost daily since. I shot a roll with it this afternoon. I went on a Leica bender in the early 2000's, trying out an M6, M4-2, M7 and MP, but sold them all after realizing I preferred the M3. I bought another M3 as back-up to my original, and I still have and use them both, with several M and LTM lenses. When Cosina first brought out the Voigtlander Bessas, I tried out a Bessa L and then Bessa T with a few of their early LTM wides; I still have them but use the lenses far more than the bodies.
I also got into the Olympus XA cameras and have owned a few of them, but have given several of them away, too. I've owned loads of other cameras, from old folders to large format gear to Polaroids and box cameras, but more of those have been given to me by various people who upon hearing that I'm a photographer who likes old cameras will hand over old stuff they have but never use. I have given away plenty of these cameras, mostly to students, but I tend not to buy stuff that's expensive (because I'm cheap and poor) and thus generally find that what I have isn't really worth the effort to sell. I did sell my first digital, a Nikon D70, after I upgraded and before it became too cheap to bother selling. The D200 I bought to replace it is sitting on a shelf upstairs as I type this, also worth so little it's hardly worth selling these days. I have a Sony A7 now as my main digital body. I have a real love/hate relationship with the thing though. The ergonomics are miserable and the menus are just awful- but it's small and the files from it are pretty nice. Most important, it plays well with loads of nice old glass I have from Nikon, Leica, Canon, Zeiss, Contax, and more; so I keep it despite its many drawbacks.
Mostly I am either given gear, or buy second hand and keep it until it's worth too little to bother selling; or I give it away to someone who seems to need it.