be careful buying a used phone.. i bought one and i went to verizon to get it activated and when i did they said it was tied to an account that was suspended and they could not activate it to my account.. i was really lucky and the person i bought it from refunded my money.. if you do get one i agree meet at a verizon store or ask for the numbers on the phone and called verizon yourself and ask if its a clean phone.
to sell i would say craigs list or ebay but also try facebook.. there are several buy/sell groups in my area that you can post stuff... thats where 90% of my buying/selling comes from!!!!!! im sure if you checked around there is a group in your area