It could work, but it would take a large amount of monitoring. For instance, if large amounts of resources are going into one account, something might be up, moniter it. Or have it less like a gift system, more like an auction house, which is less F2P friendly, thinking about it.
How about you can put up say, 5 stun guns. Someone else can either buy them straight up using crystals or credits or offer a trade. You can do one a week. The trade would have to be of an equal value. You can’t offer a zeta for 5 stun guns...
There must be a way that it can work, but more staff would be given more work for monitoring it, which could pull away fro, staff trying to make something for the game