many reason as to why buy second hand
1) vastly cheaper + sellers may have extra batteries etc
2) camera has been used a while and all things should be working fine
3) buying in person means you get a good play of the gear and know where the person selling it to you lives in case you have to return to chop their heads off for selling you a dud.
4) firmware updates have usually been released and loaded on
5) software like lightroom will already have all the codec for working on the raw files.
But before you go and hand over your cash there is something you need to assess.
Who was using the camera and how were they using it.
a camera used by a war correspondant that shot 200k photos in conditions that would make even tanks crumble... or a new dad who got a camera for xmas and quickly figured out it was far above his level to learn.
Cameras for sale with the later owner are the ones to go for.
Here are some tips when buying a Second Hand Camera
1) Buy in person.
2) Dont by total crap, if something was cheap and crap when it first came out, buying second hand at a cheaper price does not make it any less crap.
3) Double check other online prices for the item you are buying, check amazon, gumtree, ebay etc. so that even if you are getting a good deal you are not going to find a better deal just a week later online somewhere.
4) Dust and oil on the sensor is something you can complain about but very easy to fix yourself and get a better price.
5) check all the functions and dials work as expected, a lot of the time the sensor and shutter can be fine but the command dials and the power connections are the weak links.
6) If it doesnt come with a box, try and get a discount. a box is always a good thing.
7) check the connections with the lenses you have, if you have a brand new af-s vc lens check that the camera is communicating effectively with the lens so that the Vibration conpensation (reduction) is working in lens and also that the focus is working in and out accurately. a dodgy auto focus system is impossible to see just by looking, you have to test your lens on it.
8) check memory card door and slot (bent connector pins can mean your cards are not getting in)
9) make sure you get the supplied battery charger with the camera otherwise that is something you will need to buy yourself very quickly.