Is leaving feedback necessarily a good can of worms to open? While I think very highly of the person I have traded with - and would most definitely give her the highest of recommendations possible (she truly is an angel) - what happens if someone gets a poor review and disagrees with it? Would that not start a war of words or, at the very least, stir up some hard feelings? Would a rebuttal be allowed?
It seems to me, if you are concerned about trading with someone, can't you just treemail them and ask if they have traded before? If they have, can't you just contact the other member(s) (references if you will) to see if all went well? I know that I would not mind vouching for the angel that I traded with before nor would I mind if she used me as a reference.