Add clan's reputation. Only above rank 3 (for example) you can trade whit only other clan's member above the rank 3. It's an example. In this way you must play a mount of hours with your clan to be enable in trade and this would cut off items sellers or casula istant full equipped newbe players. Another cool thing could be enable the trade only in the assault with assault's drops or clan's members who had enjoy the raid/assault.