There are cameras that I'd happily sell, but their value is so low nowadays that it irks me too much to sell (example is the Nikon F4 that sold for $100 here), or it is just not worth the bother to negotiate, package, and ship.
I feel the same way on gear I paid peanuts for and could easily sell at a profit... but if I ever want to buy it again, I'd be paying the higher $... so I keep it. I still use them, though.