I'm thinking about seed and plant trading right now, in light of the recently launched Plant Lists feature. So I assumed that stetchworth was asking about a way to give feedback about trades with other members. That's what I was saying that eventually we'll probably want.
As for feedback about companies, as for specific feedback and negative reviews and things like that, I don't think I want to do that. But we are planning a "Recommendations" feature where you can give recommendations (along with reviews) about your favorite gardening companies and products.