Ideas: selling your gadgets online (The Verge)
If you are not an expert at buying/selling used/pre-owned camera gear, The Verge has published a general-interest post on selling your gadgets online. This is a general-interest post, not camera-centric, but most of today's cameras are filed under consumer electronics/gadgets. This might also be of interest if you are a buyer - so you can get a better understanding of what a seller is going through during the selling process.
On the other hand, if you don't have the time/interest/energy to maximize/optimize the returns, but instead prefer a more hassle-free approach, you can sell/trade them at B&H Photo.