Why would anyone trade for your d7100 at 600 USD if they can get it for 400 USD (you say that you can buy it at that price?) Wouldn't it make more sense for them to buy it for 400 themselves than pay you 600 for yours?
Also, if you could point out anywhere where the D7000 can be had for 600 USD, that would be nice to know. I don't see that anywhere. If you check amazon, you can get the d7100 for 499 used, the lowest d7000 is 899 right now (almost double!). I'm not sure where you get your numbers, unless things are just different in China than USA.
Edited by TWerk - 10/9/14 at 2:15pm