Well, I've got to be honest with you, the Mod Squad has talked about doing things like this in the past and we've all agreed that TeaSwap isn't really meant to be something like eBay. We don't encourage any user to try to become a 'top swapper' or make it into a mini-business, and all transactions are supposed to be privately arranged. The mods don't police the swaps or try to ensure that participants get their money/tea product as promised and our gracious host, Adagio, doesn't have much to do with it either.
So that's why we don't offer a feedback system for swaps.
However, if you have feedback you'd like to give your sender, you can send them a thank you PM or e-mail, or you can request a Mod (Mary R, Chip, or xine) to unlock the thread (if it's been locked) and you can leave feedback there.