We created this forum to make trading (e.g. Houses) easier for you guys. Here is a Quick list with the things you can and which you can't buy/sell:
Things you can buy & sell:
Houses (Donated/Undonated*)
Jailcards
Donation Points**
Things you cannot buy & sell:
Any Other Donation item
vehicles
*Undonated houses: You cannot sell an undonated house to a user that already owns an undonated house **Donation Points: You may post a buy request here and you may post an offer (If you sell donation points) [More information here]