Having a button on a trade where you can basically 'Subscribe' to the trade and it will let you know when an offer has been made of that trade. You can do it even if you haven't offered on the trade, has a way of 'keeping track' of the trade.

I don't know if its just me but I hate it when you offer on a trade and then unknowingly someone else offers and their offer gets accepted and you miss out without being able to out-bid, it's super frustrating too me, especially if you really wanted what was in the trade. And it would also be useful if you're like me and something don't know what is a suitable offer, so you can see what others offer and then offer similar.