I see people in the trading forums pretty regularly who will pay a finders fee to anybody who leads them to there rare iso.
I think it would be cool if you could have some sort of affiliate tracking per trade topic.
Say you have a rare iso. The person who finds the item in another thread, links the rare iso thread with an affiliate link.
When the person who has the item posts in the rare iso thread, there is some kind of thing that lets the buyer know who linked that person the thread.
That way there is no misunderstanding who sent the person, and whether or not they deserve the finders fee.