Hardware 1:1 System Swaps or exchanges ?

[RiiGGS]

Does anyone know of a a place where you can do 1:1 system swaps. like say a regular 3ds for a different colored one, it would have to be person to person no middle man. or if someone wants to a 3ds with a lower firmware and gives up their system that's on a newer one.
Oh and if any one with an XL on 4.0-4.5 want to trade for a Yoshi XL on 9.0.0 let me know